Pressure-sensitive adhesive sheet and pressure-sensitive adhesive composition

ABSTRACT

Provided is a pressure-sensitive adhesive composition including: an acrylic polymer (A) having a glass transition temperature lower than 0 C.°; and a polymer (B) containing, as monomer units, both a monomer (B1) having a polyorganosiloxane skeleton and a monomer (B2) whose homopolymer has a glass transition temperature of 40 C.° or higher. The acrylic polymer (A) contains, as a monomer unit, at least one monomer selected from the group consisting of N-vinyl cyclic amides represented by the following general formula (M1): 
     
       
         
         
             
             
         
       
     
     wherein R 1  is a divalent organic group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-part application of U.S.application Ser. No. 14/882,748 filed on Oct. 14, 2015, which claims thebenefit of priority from the prior Japanese Patent Application No.2013-085176, filed on Apr. 15, 2013, Japanese Patent Application No.2014-004279, filed on Jan. 14, 2014, and International PatentApplication No. PCT/JP 2014/001686, filed on Mar. 25, 2014, the entirecontent of each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a pressure-sensitive adhesivecomposition, and a pressure-sensitive adhesive layer and apressure-sensitive adhesive sheet that have the pressure-sensitiveadhesive composition.

2. Description of the Related Art

A pressure-sensitive adhesive sheet is used for adhering adherends toeach other or for fixing an article to an adherend by being firmlyadhered to the adherend. In this case, a pressure-sensitive adhesivetape having the following characteristics is required: thepressure-sensitive adhesive force of which, occurring at the beginningof attachment, is small, because it is difficult to reattach the tape ifthe tape has large pressure-sensitive adhesive force from the beginningof attachment; while the pressure-sensitive adhesive force of which isincreased over time such that large pressure-sensitive adhesive forcecan be obtained, in terms of fixing members in home electricalappliances and mobile devices, etc.

In order to meet such a change in pressure-sensitive adhesive force,methods for changing the pressure-sensitive adhesive force ofpressure-sensitive adhesive sheets by heating or ultraviolet irradiationhave traditionally been used (see Patent Documents 1 to 3).

A pressure-sensitive adhesive sheet having the following properties isalso required: when a pressure-sensitive adhesive sheet is peeled froman adherend, the adherend is hard to be contaminated or there is littleadhesive deposit remaining on the adherend.

-   -   [Patent Document 1] Japanese Patent Application Publication No.        1999-302610    -   [Patent Document 2] Japanese Patent Application Publication No.        1999-302614    -   [Patent Document 3] Japanese Patent Application Publication No.        2011-127054

There has been the problem that the method for changing thepressure-sensitive adhesive force of a pressure-sensitive adhesive sheetby heating or ultraviolet irradiation cannot be applied to an adherendthat may be adversely affected by these treatments. There is actually amethod for reducing pressure-sensitive adhesive force by temporarilyforming a layer having small cohesive force on the interface between apressure-sensitive adhesive and an adherend with the use of an additive,etc.; in such a method, however, there occurs the problem that, after apressure-sensitive adhesive sheet is peeled in the state where thepressure-sensitive adhesive force is small, the adherend may becontaminated by adhesive deposit or attached additives, which causes theadherend to be adversely affected or makes it difficult to reuse theadherend. Accordingly, in a traditional pressure-sensitive adhesive,reworkability to various adherends, which is obtained by smallpressure-sensitive adhesive force occurring at the beginning ofattachment, an increase in adhesiveness occurring over time, and a lowcontamination property have not been entirely achieved.

SUMMARY OF THE INVENTION

The present invention has been made in view of these problems, and apurpose of the invention is to provide a pressure-sensitive adhesive inwhich reworkability to an adherend, an improvement in adhesivenessoccurring over time, and a low contamination property can be entirelyachieved.

An aspect of the present invention is a pressure-sensitive adhesivecomposition. The pressure-sensitive adhesive composition comprises: apolymer (A) having a glass transition temperature lower than 0 C.°; anda polymer (B) containing, as a monomer unit, a monomer (B1) having apolyorganosiloxane skeleton.

In some embodiments, the polymer (B) may further contain a monomer whosehomopolymer has a glass transition temperature of 40 C.° or higher.

In some embodiments, the polymer (A) may contain, as a monomer unit, atleast one monomer selected from the group consisting of N-vinyl cyclicamides, typically represented by the following general formula (M1).

(R¹ in the general formula (M1) is a divalent organic group.)

In some embodiments, the monomer (B1) having a polyorganosiloxaneskeleton may have a functional group equivalent (Fge) of, for instance,1000 g/mol≤Fge<15000 g/mol. In some embodiments, the polymer (B) mayhave a weight average molecular weight (MwB) of, for instance,10000≤MwB<100000.

In some embodiments, the content of the polymer (B) may be, forinstance, 0.1 to 20 parts by mass, relative to 100 parts by mass of thepolymer (A).

In the pressure-sensitive adhesive composition of the aforementionedaspect, the polymer (A) may be an acrylic polymer. The polymer (B) maybe a polymer containing, as a monomer unit, 10% by mass to 80% by massof a monomer whose homopolymer has a glass transition temperature of 40°C. or higher.

Additionally, the monomer having a polyorganosiloxane skeleton may beone or more monomers selected from the group consisting of the monomersrepresented by the following general formula (1) or (2):

[wherein, R₃ is hydrogen or methyl; R₄ is methyl or a monovalent organicgroup; and each of m and n is an integer of 0 or more.]

Another aspect of the present invention is a pressure-sensitive adhesivelayer. The pressure-sensitive adhesive layer is made of thepressure-sensitive adhesive composition according to any one of theaforementioned aspects.

Still another aspect of the present invention is a pressure-sensitiveadhesive sheet. The pressure-sensitive adhesive sheet is made by forminga pressure-sensitive adhesive layer of the aforementioned aspect on atleast one surface of a supporting body.

Appropriate combinations of the aforementioned respective elements willalso be within the scope of the present invention sought to be protectedby the patent application.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention. Hereinafter, preferredembodiments for carrying out the present invention will be described indetail with reference to the accompanying tables.

A pressure-sensitive adhesive composition according to an embodimentcomprises a polymer (A) and a polymer (B).

Hereinafter, each component that forms the pressure-sensitive adhesivecomposition according to the embodiment will be described in detail.

[Polymer (A)]

The polymer (A) is a polymer having a glass transition temperature lowerthan 0° C. The polymer (A) is not particularly limited as far as theglass transition temperature of which is lower than 0° C., and variouspolymers to be generally used as a pressure-sensitive adhesive, such asan acrylic polymer, rubber polymer, silicone polymer, polyurethanepolymer, and polyester polymer, can be used. When the polymer (B) is a(meth)acrylic polymer, an acrylic polymer, which is easily compatiblewith the (meth)acrylic polymer and has high transparency, is preferable.

The glass transition temperature (Tg) of the polymer (A) isadvantageously lower than 0 C.°. When the glass transition temperature(Tg) of the polymer (A) is lower than 0 C.°, the pressure-sensitiveadhesive containing the polymer (A) tend to exhibit moderate fluidity,and therefore, it is suited for pressure-sensitive adhesive that canexhibit an increase in pressure-sensitive adhesive force occurring overtime. The glass transition temperature (Tg) of the polymer (A) ispreferably lower than −10 C.°, and more preferably lower than −40 C.°and usually −80 C.° or higher.

The glass transition temperature is a nominal value described indocuments or catalogs, etc., or a value calculated based on thefollowing equation (X) (Fox Equation).

1/Tg=W₁/Tg₁+W₂/Tg₂+ . . . +W_(n)/Tg_(n)  (X)

[wherein, Tg represents the glass transition temperature (unit: K) ofthe polymer (A); Tg_(i) (i=1, 2, . . . n) represents the glasstransition temperature (unit: K), when monomer i forms a homopolymer;and W_(i) (i=1, 2, . . . n) represents the mass fraction of the monomeri based on the total monomer components.] The above equation (X) isadopted when the polymer (A) is formed of n types of monomer componentsof monomer 1, monomer 2, . . . , monomer n.

In the present description, the “glass transition temperature when ahomopolymer is formed” means the “glass transition temperature of ahomopolymer of the monomer”, which means the glass transitiontemperature (Tg) of a polymer formed only by a monomer (sometimesreferred to as a “monomer X”) as a monomer component. Specifically,those values are described in “Polymer Handbook” (Third Edition, JohnWiley & Sons, Inc, 1989). The glass transition temperatures (Tg) ofhomopolymers, which are not described in the above document, means thevalues obtained, for example, by the following measuring method. Thatis, into a reactor provided with a thermometer, a stirrer, a nitrogeninlet pipe, and a reflux cooling pipe, 100 parts by mass of the monomerX, 0.2 parts by mass of 2,2′-azobisisobutyronitrile, and 200 parts bymass of ethyl acetate as a polymerization solvent are placed, and themixture is stirred for 1 hour while nitrogen gas is being introduced.After the oxygen in the polymerization system is removed in this way,the mixture is heated to 63° C. to react with each other for 10 hours.Subsequently, the mixture is cooled to room temperature to obtain ahomopolymer solution having a solid concentration of 33% by mass.Subsequently, this homopolymer solution is caused to flow on a releaseliner to be coated thereon, and the solution is then dried to make atest sample (sheet-shaped homopolymer) having a thickness ofapproximately 2 mm. Subsequently, 1 to 2 mg of this test sample isweighed and placed in an aluminum open cell, so that Reversing Heat Flow(specific heat component) behaviors of the homopolymer are obtained byusing a temperature-modulated DSC (product name: “Q-2000” made by TAInstruments Inc.) at a heating rate of 5° C./min under 50 ml/min of anitrogen flow rate atmosphere. With reference to JIS-K-7121, thetemperature at the point where a straight line, located at the samedistance in the vertical axis direction from a straight line obtained byextending the base line on the low-temperature side of the obtainedReversing Heat Flow and from a straight line obtained by extending thebase line on the high-temperature side thereof, and a curved line,located at the portion where the glass transition temperature is changedin a stepwise shape, intersect with each other is determined to be theglass transition temperature (Tg) of the homopolymer.

While no particular limitations are imposed, the weight averagemolecular weight (MwA) of the polymer (A) can be, for example,approximately 3×10⁴ or higher. The weight average molecular weight (MwA)of the polymer (A) may be suitably about 10×10⁴ or higher and preferablyabout 20×10⁴ or higher. With the polymer (A) having such a MwA, apressure-sensitive adhesive having a suitable cohesion is likely to beobtained. From the standpoint of obtaining higher cohesiveness, in someembodiments, the weight average molecular weight (MwA) of the polymer(A) can be, for example, about 30×10⁴ or higher, about 40×10⁴ or higher,about 50×10⁴ or higher, about 60×10⁴ or higher, or even about 80×10⁴ orhigher. The weight average molecular weight (MwA) of the polymer (A) isnormally suitably about 500×10⁴ or lower. The polymer (A) having such aMwA is suited for obtaining a pressure-sensitive adhesive sheetexhibiting a low pressure-sensitive adhesive force to an adherend at thebeginning of attachment and an increase in pressure-sensitive adhesiveforce occurring over time. The MwA being not excessively high can beadvantageous also from the standpoint of improving compatibility withthe polymer (B). In some embodiments, the weight average molecularweight (MwA) of the polymer (A) can be, for example, about 250×10⁴ orlower, about 200×10⁴ or lower, or even about 150×10⁴ or lower.

[Acrylic Polymer]

Hereinafter, an acrylic polymer, which is a preferred specific exampleof the polymer (A), will be described in detail.

As used herein, the term “acrylic polymer” refers to a polymer having amonomeric unit derived from a (meth)acrylic monomer in the polymerstructure and typically refers to a polymer containing over 50% by massmonomeric units derived from a (meth)acrylic monomer. The term“(meth)acrylic monomer” refers to a monomer having at least one(meth)acryloyl group in one molecule. In this context, it is intendedthat the term “(meth)acryloyl group” collectively refers to an acryloylgroup and a methacryloyl group. Therefore, the concept of “(meth)acrylicmonomer” as used herein may encompass both a monomer (acrylic monomer)having an acryloyl group and a monomer (methacrylic monomer) having amethacryloyl group. Similarly, it is intended that the term“(meth)acrylic acid” as used herein collectively refers to acrylic acidand methacrylic acid and the term “(meth)acrylate” collectively refersto an acrylate and a methacrylate.

The acrylic polymer can be, for instance, a polymer containing, as amonomer unit, a (meth)acrylic acid alkyl ester having a C₁₋₂₀ linear orbranched alkyl group in an amount of 50% by mass or more. Solely onespecies or a combination of two or more species of the (meth)acrylicacid alkyl ester having a C₁₋₂₀ alkyl group may be used to form theacrylic polymer. A method of obtaining the acrylic polymer is notparticularly limited, but the polymer can be obtained by applyingvarious polymerization methods that are generally used as a method ofsynthesizing an acrylic polymer, such as solution polymerization,emulsion polymerization, block polymerization, suspensionpolymerization, and radiation curing polymerization.

The ratio of the (meth)acrylic acid alkyl ester having a C₁₋₂₀ linear orbranched alkyl group to the total mass of the monomer components forpreparing the acrylic polymer can be, for instance, 50% by mass to 99.9%by mass, preferably 60% by mass to 98% by mass, and more preferably 70%by mass to 95% by mass.

Examples of the (meth)acrylic acid alkyl ester having a C₁₋₂₀ linear orbranched alkyl group include (meth)acrylic acid C₁₋₂₀ alkyl esters(preferably (meth)acrylic acid C₂₋₁₄ alkyl esters, and more preferably(meth)acrylic acid C₂₋₁₀ alkyl esters), such as, for example,(meth)acrylic acid methyl, (meth)acrylic acid ethyl, (meth)acrylic acidpropyl, (meth)acrylic acid isopropyl, (meth)acrylic acid butyl,(meth)acrylic acid isobutyl, (meth)acrylic acid s-butyl, (meth)acrylicacid t-butyl, (meth)acrylic acid pentyl, (meth)acrylic acid isopentyl,(meth)acrylic acid hexyl, (meth)acrylic acid heptyl, (meth)acrylic acidoctyl, (meth)acrylic acid 2-ethylhexyl, (meth)acrylic acid isooctyl,(meth)acrylic acid nonyl, (meth)acrylic acid isononyl, (meth)acrylicacid decyl, (meth)acrylic acid isodecyl, (meth)acrylic acid undecyl,(meth)acrylic acid dodecyl, (meth)acrylic acid tridecyl, (meth)acrylicacid tetradecyl, (meth)acrylic acid pentadecyl, (meth)acrylic acidhexadecyl, (meth)acrylic acid heptadecyl, (meth)acrylic acid octadecyl,(meth)acrylic acid isooctadecyl, (meth)acrylic acid nonadecyl, and(meth)acrylic acid eicosyl. Herein, the (meth)acrylic acid alkyl estermeans an acrylic acid alkyl ester and/or a methacrylic acid alkyl ester,and all of the “(meth) . . . ” expressions have the same meaning.

The acrylic polymer may contain another monomer component(copolymerizable monomer) that is copolymerizable with the (meth)acrylicacid alkyl ester, if necessary, in order to improve cohesive force, heatresistance, and a bridging characteristic, etc. Accordingly, the acrylicpolymer may contain a copolymerizable monomer along with the(meth)acrylic acid alkyl ester as a major component. A monomer having apolar group can be preferably used as the copolymerizable monomer.

Specific examples of the copolymerizable monomer include: carboxylgroup-containing monomers, such as acrylate, methacrylic acid,carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleicacid, fumaric acid, crotonic acid, and isocrotonic acid; hydroxylgroup-containing monomers, such as (meth)acrylic acid hydroxyalkylsincluding (meth)acrylic acid 2-hydroxyethyl, (meth)acrylic acid2-hydroxypropyl, (meth)acrylic acid 2-hydroxybutyl, (meth)acrylic acid3-hydroxypropyl, (meth)acrylic acid 4-hydroxybutyl, (meth)acrylic acid6-hydroxyhexyl, (meth)acrylic acid 8-hydroxyoctyl, (meth)acrylic acid10-hydroxydecyl, (meth)acrylic acid 12-hydroxy lauryl, and(4-hydroxymethyl cyclohexyl)methyl methacrylate, etc.; acid anhydridegroup-containing monomers, such as maleic acid anhydride and itaconicacid anhydride; sulfonic group-containing monomers, such asstyrenesulfonic acid, allylsulfonic acid,2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamidepropanesulfonic acid, sulfopropyl(meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid; phosphate group-containing monomers, such as2-hydroxyethyl acryloyl phosphate; (N-substituted)amide monomers, suchas (meth)acrylamide, N,N-dialkyl(meth)acrylamides includingN,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide,N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide,N,N-di(n-butyl)(meth)acrylamide, and N,N-di(t-butyl)(meth)acrylamide,etc., N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide,N-butyl(meth)acrylamide, N-n-butyl(meth)acrylamide,N-methylol(meth)acrylamide, N-ethylol(meth)acrylamide, N-methylolpropane (meth)acrylamide, N-methoxymethyl(meth)acrylamide,N-methoxyethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, andN-acryloyl morpholine; succinimide monomers, such as N-(meth)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxy hexamethylene succinimide,and N-(meth)acryloyl-8-oxy hexamethylene succinimide; maleimidemonomers, such as N-cyclohexyl maleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenyl maleimide; itaconimide monomers, such asN-methylitaconimide, N-ethylitaconimide, N-butylitaconimide,N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide,and N-laurylitaconimide; vinyl esters, such as vinyl acetate and vinylpropionate; nitrogen-containing heterocyclic monomers, such asN-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine,N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine,N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole,N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine,N-(meth)acryloyl pyrrolidine, N-vinyl morpholine, N-vinyl-2-piperidone,N-vinyl-3-morpholinone, N-vinyl-2-caprolactam,N-vinyl-1,3-oxazine-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinyl isoxazole, N-vinyl thiazole, N-vinyl isothiazole, andN-vinyl pyridazine; N-vinyl carboxylic acid amides; lactam monomers,such as N-vinyl caprolactam; cyano-containing monomers, such asacrylonitrile and methacrylonitrile; (meth)acrylic acid aminoalkylmonomers, such as (meth)acrylic acid aminoethyl, (meth)acrylic acidN,N-dimethylaminoethyl, (meth)acrylic acid N,N-dimethylaminoethyl, and(meth)acrylic acid t-butylaminoethyl; (meth)acrylic acid alkoxy alkylmonomers, such as (meth)acrylic acid methoxyethyl, (meth)acrylic acidethoxyethyl, (meth)acrylic acid propoxyethyl, (meth)acrylic acidbutoxyethyl, and (meth)acrylic acid ethoxypropyl; styrene monomers, suchas styrene and α-methylstyrene; epoxy group-containing acrylic monomers,such as (meth)acrylic acid glycidyl; acrylic acid ester monomers havinga heterocycle, halogen atom, silicon atom, or the like, such as(meth)acrylic acid tetrahydrofurfuryl, fluorine atom-containing(meth)acrylate, and silicone(meth)acrylate; olefin monomers, such asisoprene, butadiene, and isobutylene; vinyl ether monomers, such asmethyl vinyl ether and ethyl vinyl ether; vinyl esters, such as vinylacetate and vinyl propionate; aromatic vinyl compounds, such as vinyltoluene and styrene; olefins or dienes, such as ethylene, butadiene,isoprene, and isobutylene; vinyl ethers, such as vinyl alkyl ether;vinyl chloride; sulfonic acid group-containing monomers, such as vinylsulfonate sodium; imide group-containing monomers, such as cyclohexylmaleimide and isopropyl maleimide; isocyanate group-containing monomers,such as 2-isocyanate ethyl(meth)acrylate; acryloyl morpholine;(meth)acrylic acid esters having an alicyclic hydrocarbon group, such ascyclopentyl(meth)acrylate, cyclohexyl(meth)acrylate,isobornyl(meth)acrylate, and dicyclopentanyl(meth)acrylate;(meth)acrylic acid esters having an aromatic hydrocarbon group, such asphenyl(meth)acrylate, and phenoxyethyl(meth)acrylate; (meth)acrylic acidesters obtained from terpene compound derivative alcohols; and the like.These copolymerizable monomers can be used alone or in combination oftwo or more thereof.

In the pressure-sensitive adhesive composition of the aforementionedaspect, it is preferable that the acrylic polymer contains, as a monomerunit, at least one monomer selected from the group consisting of N-vinylcyclic amides (for instance, N-vinyl cyclic amides represented by thefollowing general formula (M1)) and hydroxyl group-containing monomers.

-   -   (R¹ in the formula (M1) is a divalent organic group.)

It is particularly preferable to contain at least one monomer selectedfrom the group consisting of the N-vinyl cyclic amides. The acrylicpolymer may contain, as a monomer unit, both a monomer selected from thegroup consisting of the N-vinyl cyclic amides and a monomer selectedfrom hydroxyl group-containing monomers.

Specific examples of the N-vinyl cyclic amides includeN-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-3-morpholinone,N-vinyl-2-caprolactam, N-vinyl-1,3-oxazine-2-one, andN-vinyl-3,5-morpholinedione, etc. Among them, N-vinyl-2-pyrrolidone andN-vinyl-2-caprolactam are particularly preferred.

The use amount of N-vinyl cyclic amides is not particularly limited, butN-vinyl cyclic amides can be contained in an amount of usually 0.01% bymass or more, preferably 0.1% by mass or more, and more preferably 0.5%by mass or more, based on the total mass of the monomer components forpreparing the acrylic polymer. In some embodiments, N-vinyl cyclicamides can be contained in an amount of usually 40% by mass or less,preferably 30% by mass or less, and more preferably 20% by mass or less,based on the total mass of the monomer components for preparing theacrylic polymer.

In addition, the use amount of copolymerizable monomer is notparticularly limited, but copolymerizable monomers can be contained inan amount of usually 0.01% by mass or more, preferably 0.1% by mass ormore, and more preferably 0.5% by mass or more, based on the total massof the monomer components for preparing the acrylic polymer. In someembodiments, the copolymerizable monomers can be contained in an amountof 40% by mass or less, preferably 30% by mass or less, and morepreferably 20% by mass or less, based on the total mass of the monomercomponents for preparing the acrylic polymer.

As specific examples of the hydroxyl group-containing monomers,(meth)acrylic acid 2-hydroxyethyl, (meth)acrylic acid 4-hydroxybutyl,and (meth)acrylic acid 6-hydroxyhexyl, etc., can be preferably used. Theuse amount of the hydroxy group-containing monomer is not particularlylimited, but a copolymerizable monomer can be used in an amount ofusually 40% by mass or less, preferably 20% by mass or less, and morepreferably 10% by mass, based on the total mass of the monomercomponents for preparing the acrylic polymer.

By containing 0.01% by mass or more of the copolymerizable monomer, itcan be prevented that the cohesive force of the pressure-sensitiveadhesive sheet having a pressure-sensitive adhesive layer formed by theacrylic pressure-sensitive adhesive composition may be decreased.Further, by containing 40% by mass or less of the copolymerizablemonomer, it can be prevented that the cohesive force thereof may becometoo large, and the tackiness at normal temperature (25° C.) can beimproved.

In the present embodiment, when the pressure-sensitive adhesive sheet isused in a metal adherend or an adherend on which a metal film is formed(e.g., a touch panel, etc., on which a conductive film (ITO) is formed),it is desirable that a carboxyl group is not contained in the acrylicpolymer. Also, from the viewpoint of corrosiveness, it is desirable thatacidic functional groups, other than a carboxyl group, are notsubstantially contained therein. Accordingly, the monomer units thatform the acrylic polymer of the present embodiment may not substantiallycontain a monomer having a carboxyl group or an acidic functional groupother than a carboxyl group.

The acidic functional group means a functional group having activehydrogen. Examples of the acidic functional group include, for example,a carboxyl group, sulfonate group, phosphate group, etc. The expressionthat acidic functional groups “are not substantially contained” meansthat they are not actively combined, except the case where they areinevitably mixed. Specifically, it is meant that the ratio (% by mass)of a monomer having an acidic functional group to the total mass ofunits for forming the acrylic polymer is less than 1% by mass, andpreferably less than 0.5% by mass.

Additionally, the acrylic polymer may contain, if necessary, apolyfunctional monomer for adjusting the cohesive force of thepressure-sensitive adhesive composition to be formed.

Examples of the polyfunctional polymer include, for example:(poly)ethylene glycol di(meth)acrylate, (poly)propylene glycoldi(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritoldi(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritolhexa(meth)acrylate, 1,2-ethylene glycol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropanetri(meth)acrylate, tetramethylol methane tri(meth)acrylate,allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, epoxyacrylate, polyester acrylate, urethane acrylate,butyldiol(meth)acrylate, and hexyldiol(meth)acrylate, etc. Among them,trimethylolpropane tri(meth)acrylate, hexanediol di(meth)acrylate, anddipentaerythritol hexa(meth)acrylate can be preferably used. Thepolyfunctional monomers can be used alone or in combination of two ormore thereof.

The use amount of the polyfunctional monomer may vary depending on themolecular weight or the number of functional groups thereof, but it isusually suitably in a range of about 0.01 part to 3.0 parts by mass to100 parts by mass of the acrylic polymer. In some embodiments, theamount of polyfunctional monomer used to 100 parts by mass of theacrylic polymer can be, for instance, 0.02 part by mass or greater, oreven 0.03 part by mass or greater. With increasing amount ofpolyfunctional monomer used, the pressure-sensitive adhesive force atthe beginning of attachment tends to be lower and the reworkabilitytends to be improved. On the other hand, from the standpoint ofremaining moderate fluidity for facilitating an increase inpressure-sensitive adhesive force occurring over time, the amount ofpolyfunctional monomer used to 100 parts by mass of the acrylic polymercan be 2.0 parts by mass or less, 1.0 part by mass or less, or even 0.5part by mass or less.

From the standpoint of facilitating to obtain a pressure-sensitiveadhesive sheet favorably combining the low pressure-sensitive adhesiveforce at the beginning of attachment with an increase inpressure-sensitive adhesive force occurring over time, in someembodiments, the use amount of the polyfunctional monomer is suitably0.01% by mass to 3.0% by mass, preferably 0.02% by mass to 2.0% by mass,and more preferably 0.03% by mass to 1.0% by mass, based on the totalmass of the monomer components for preparing the acrylic polymer.

In preparing the acrylic polymer, the acrylic polymer can be easilyformed by a curing reaction using heat or ultraviolet rays with the useof a polymerization initiator, such as a thermal polymerizationinitiator, photo-polymerization initiator (photo-initiator), or thelike. In particular, photo-polymerization can be preferably used fromthe advantage that a pressure-sensitive adhesive property is improved,etc. The polymerization initiators can be used alone or in combinationof two or more thereof.

Examples of the thermal polymerization initiator include, for example:azo polymerization initiators (e.g., 2,2′-azobisisobutyronitrile,2,2′-azobis-2-methylbutyronitrile, 2,2′-azobis(2-methylpropionicacid)dimethyl, 4,4′-azobis-4-cyanovalerianic acid, azobisisovaleronitrile, 2,2′-azobis(2-amidinopropane)dihydrochloride,2,2′-azobis[2-(5-methyl-2-imidazoline-2-yl) propane] dihydrochloride,2,2′-azobis(2-methylpropionamidine)disulfate, and 2,2′-azobis

(N,N′-dimethyleneisobutylamidine)dihydrochloride, etc.);

peroxide polymerization initiators (e.g., dibenzoyl peroxide, t-butylpermaleate, and lauroyl peroxide, etc.); redox polymerizationinitiators; and the like.

The use amount of the thermal polymerization initiator is notparticularly limited, but the thermal polymerization initiator iscombined, for example, in an amount of 0.01 parts by mass to 5 parts bymass, and preferably 0.05 parts by mass to 3 parts by mass, based on 100parts by mass of the monomer components for preparing the acrylicpolymer.

The photo-polymerization initiator is not particularly limited, but, forexample, a benzoin ether photo-polymerization initiator, acetophenonephoto-polymerization initiator, α-ketol photo-polymerization initiator,aromatic sulfonyl chloride photo-polymerization initiator, photoactiveoxime photo-polymerization initiator, benzoin photo-polymerizationinitiator, benzyl photo-polymerization initiator, benzophenonephoto-polymerization initiator, ketal photo-polymerization initiator,thioxanthone photo-polymerization initiator, acylphosphine oxidephoto-polymerization initiator, or the like, can be used.

Specific examples of the benzoin ether photo-polymerization initiatorinclude, for example, benzoin methyl ether, benzoin ethyl ether, benzoinpropyl ether, benzoin isopropyl ether, benzoin isobutyl ether,2,2-dimethoxy-1,2-diphenylethane-1-one [product name: IRGACURE 651 madeby BASF], and Anisoin, etc. Specific examples of the acetophenonephoto-polymerization initiator include, for example, 1-hydroxycyclohexylphenyl ketone [product name: IRGACURE 184, made by BASF], 4-phenoxydichloroacetophenone, 4-t-butyl-dichloroacetophenone,1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one[product name: IRGACURE 2959, made by BASF],2-hydroxy-2-methyl-1-phenyl-propane-1-one [product name: DAROCUR 1173,made by BASF], and methoxy acetophenone, etc. Specific examples of theα-ketol photo-polymerization initiator include, for example,2-methyl-2-hydroxy propiophenone and1-[4-(2-hydroxyethyl)-phenyl]-2-hydroxy-2-methylpropane-1-one, etc.Specific examples of the aromatic sulfonyl chloride photo-polymerizationinitiator include, for example, 2-naphthalene sulfonyl chloride, etc.Specific examples of the photoactive oxime photo-polymerizationinitiator include, for example,1-phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)-oxime, etc.

Specific examples of the benzoin photo-polymerization initiator include,for example, benzoin, etc. Specific examples of the benzylphoto-polymerization initiator include, for example, benzyl, etc.Specific examples of the benzophenone photo-polymerization initiatorsinclude, for example, benzophenone, benzoylbenzoic acid,3,3′-dimethyl-4-methoxybenzophenone, polyvinyl benzophenone, andα-hydroxy cyclohexyl phenyl ketone, etc. Specific examples of the ketalphoto-polymerization initiator include, for example, benzyl dimethylketal, etc. Specific examples of the thioxanthone photo-polymerizationinitiato include, for example, thioxanthone, 2-chlorothioxanthone,2-methyl thioxanthone, 2,4-dimethyl thioxanthone, isopropylthioxanthone, 2,4-dichloro thioxanthone, 2,4-diethyl thioxanthone,isopropyl thioxanthone, 2,4-diisopropyl thioxanthone, and dodecylthioxanthone, etc.

Specific examples of the acylphosphine photo-polymerization initiatorinclude, for example, bis(2,6-dimethoxybenzoyl)phenylphosphine oxide,bis(2,6-dimethoxybenzoyl)(2,4,4-trimethylpentyl) phosphine oxide,bis(2,6-dimethoxybenzoyl)-n-butyl phosphine oxide,bis(2,6-dimethoxybenzoyl)-(2-methylpropane-1-yl)phosphine oxide,bis(2,6-dimethoxybenzoyl)-(1-methylpropane-1-yl) phosphine oxide,bis(2,6-dimethoxybenzoyl)-t-butylphosphine oxide,bis(2,6-dimethoxybenzoyl)cyclohexylphosphine oxide,bis(2,6-dimethoxybenzoyl)octylphosphine oxide,bis(2-methoxybenzoyl)(2-methylpropane-1-yl)phosphine oxide,bis(2-methoxybenzoyl)(1-methylpropane-1-yl)phosphine oxide,bis(2,6-diethoxybenzoyl)(2-methylpropane-1-yl)phosphine oxide,bis(2,6-diethoxybenzoyl)(1-methylpropane-1-yl) phosphine oxide,bis(2,6-dibutoxybenzoyl)(2-methylpropane-1-yl) phosphine oxide,bis(2,4-dimethoxybenzoyl)(2-methypropane-1-yl) phosphine oxide,bis(2,4,6-trimethylbenzoyl)(2,4-dipentoxyphenyl) phosphine oxide,bis(2,6-dimethoxybenzoyl)benzyl phosphine oxide,bis(2,6-dimethoxybenzoyl)-2-phenylpropyl phosphine oxide,bis(2,6-dimethoxybenzoyl)-2-phenylethyl phosphine oxide,bis(2,6-dimethoxybenzoyl)benzyl phosphine oxide,bis(2,6-dimethoxybenzoyl)-2-phenylpropyl phosphine oxide,bis(2,6-dimethoxybenzoyl)-2-phenylethyl phosphine oxide,2,6-dimethoxybenzoyl benzylbutylphosphine oxide, 2,6-dimethoxybenzoylbenzyloctylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-2,5-diisopropylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-2-methylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-4-methylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-2,5-diethylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-2,3,5,6-tetramethylphenylphosphin e oxide,bis(2,4,6-trimethyl benzoyl)-2,4-di-n-butoxy phenylphosphine oxide,2,4,6-trimethylbenzoyl diphenylphosphine oxide,bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide,bis(2,4,6-trimethylbenzoyl)isobutylphosphine oxide,2,6-dimethoxybenzoyl-2,4,6-trimethylbenzoyl-n-butylphosphine oxide,bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-2,4-dibutoxyphenylphosphine oxide,1,10-bis[bis(2,4,6-trimethylbenzoyl)phosphine oxide]decane, andtri(2-methylbenzoyl)phosphine oxide, etc.

The use amount of the photo-polymerization initiator is not particularlylimited and can be selected so that a polymerization reaction proceedsproperly. In some embodiments, the photo-polymerization initiator can beused, for example, in an amount of 0.01 part by mass to 5 parts by mass,and preferably 0.05 part by mass to 3 parts by mass, based on 100 partsby mass of the monomer components for preparing the acrylic polymer.

The photo-polymerization initiators can be used alone or in combinationof two or more thereof.

In the present embodiment, the polymer (A) can also be prepared as apartial polymer (acrylic polymer syrup) whose monomer components arepartially polymerized by irradiating a mixture, in which the monomercomponents and the polymerization initiator have been blended, withultraviolet (UV) rays. The polymerization of the acrylic polymer syrupcan be completed by blending the later-described polymer (B) into thesyrup to prepare a pressure-sensitive adhesive composition and then bycoating the pressure-sensitive adhesive composition onto a predeterminedobject to be coated followed by irradiation of ultraviolet rays.

That is, the acrylic polymer syrup is a precursor of the polymer (A),and accordingly a composition, in which the polymer (B) has been blendedinto the acrylic polymer syrup, also corresponds to thepressure-sensitive adhesive composition of the present embodiment.

[Polymer (B)]

The polymer (B) contains, as a monomer unit, a monomer (B1) having apolyorganosiloxane skeleton. With the mobility and low polarity of thesiloxane structure derived from the monomer (B1), the polymer (B) mayserve as an adhesive strength rise retarder that contributes to a lowerpressure-sensitive adhesive force at the beginning of attachment and toan increase in pressure-sensitive adhesive force occurring over time.

The monomer (B1) having a polyorganosiloxane skeleton that forms thepolymer (B) is not particularly limited, but any polyorganosiloxaneskeleton-containing monomer can be used. Due to the low polarityattributed to its structure, the monomer (B1) having apolyorganosiloxane skeleton facilitates concentration of the polymer (B)in the pressure-sensitive adhesive layer surface of thepressure-sensitive adhesive sheet prior to use (before applied to anadherend), thereby exhibiting light release (low adhesiveness) at thebeginning of attachment to the adherend. A mono-terminally reactivemonomer having a polyorganosiloxane skeleton can preferably be used forthe monomer (B1). By using the monomer (B1) which is mono-terminallyreactive, a polymer (B) having a siloxane structure in a side chain canbe obtained. The use of the polymer (B) having such a structure mayfacilitate obtaining a pressure-sensitive adhesive sheet favorablycombining the low pressure-sensitive adhesive force at the beginning ofattachment with an increase in pressure-sensitive adhesive forceoccurring over time, due to the mobility of the polymer (B) and themotility of its side chain.

As specific examples of the polyorganosiloxane skeleton-containingmonomer, for example, the polyorganosiloxane skeleton-containingmonomers represented by the following general formula (1) or (2) can beused. More specifically, one-terminal reactive silicone oil made byShin-Etsu Chemical Co., Ltd., such as X-22-174ASX, X-22-174DX,X-22-2426, and X-22-2475, can be cited, which can be used alone or incombination of two or more thereof.

[wherein, R₃ is hydrogen or methyl; R₄ is methyl or a monovalent organicgroup; and each of m and n is an integer of 0 or more.]

The functional group equivalent (Fge) of the monomer (B1) having apolyorganosiloxane skeleton that forms the polymer (B) is notparticularly limited to a specific range and can be selected so that thedesired effect with the use of the monomer (B1) may preferably beobtained. In some embodiments, from the standpoint of the ease ofsufficiently suppressing the pressure-sensitive adhesive force at thebeginning of the attachment, the Fge of the monomer (B1) can be 140g/mol or greater, 200 g/mol or greater, and normally advantageously 300g/mol or greater (for instance, 500 g/mol or greater). In someembodiments, the Fge of the monomer (B1) can be suitably 700 g/mol orgreater, preferably 800 g/mol or greater, more preferably 850 g/mol orgreater, yet more preferably 1000 g/mol or greater, or particularlypreferably 1500 g/mol or greater. In some embodiments, from thestandpoint of facilitating to obtain a pressure-sensitive adhesive sheetfavorably combining the low pressure-sensitive adhesive force at thebeginning of attachment with an increase in pressure-sensitive adhesiveforce occurring over time, the Fge of the monomer (B1) can be 2500 g/molor greater, 3000 g/mol or greater, 4500 g/mol or greater, 6000 g/mol orgreater, 9000 g/mol or greater, 12000 g/mol or greater, or even 15000g/mol or greater (for instance, 16000 g/mol or greater). The Fge of themonomer (B1) can be, for instance, about 50000 g/mol or less. From thestandpoint of facilitating an increase in pressure-sensitive adhesiveforce occurring over time, the Fge of the monomer (B1) can be, forinstance, preferably 30000 g/mol or less, more preferably 20000 g/mol orless. In some embodiments, the Fge of the monomer (B1) can be less than18000 g/mol, less than 15000 g/mol, less than 10000 g/mol, less than6000 g/mol, or even less than 5000 g/mol.

Herein, the “functional group equivalent” means the mass of a mainskeleton (e.g., polydimethylsiloxane) bound to per functional group. Theindicated unit of g/mol is obtained by converting into 1 mol offunctional groups. The functional group equivalent of a monomer having apolyorganosiloxane skeleton is calculated from spectral intensities in¹H-NMR (proton NMR) obtained, for example, by a nuclear magneticresonance (NMR) apparatus.

The ratio of the spectral intensity of H bound to Si of a siloxanestructure via C (e.g., H in Si—(CH₃)₂) to the spectral intensity of H ina functional group of C—CH₃, SH, or C═CH₂ is determined in ¹H-NMRobtained.

When the case is described as an example, where the ratio of thespectral intensity of H in a siloxane structure of Si—(CH₃)₂ to that ofH in a functional group of C═CH₂ is determined, the ratio of the numberof siloxane structures of Si—(CH₃)₂ to that of functional groups ofC═CH₂, both being contained in a measurement sample, can be determinedfrom the ratio of the spectral intensities.

Because the chemical formula of the siloxane structure and that of thefunctional group are known in advance, the ratio (A/B) of the number Aof the siloxane structures each having an Si—(CH₃)₂ bond to the number Bof the functional groups, the siloxane structures and the functionalgroups being contained in the measurement sample, can be determined fromthe ratio of the number of the siloxane structures of Si—(CH₃)₂ to thenumber of the functional groups of C═CH₂.

Because the molecular weight per one siloxane structure having anSi—(CH₃)₂ bond (herein, dimethylsiloxane) is known, the value, obtainedby multiplying the molecular weight per one siloxane structure with theratio (A/B) of the number A of the siloxane structures to the number ofthe functional groups, becomes the mass of the siloxane structure havingan Si—(CH₃)₂ bond per one functional group, i.e., the mass of a mainskeleton, and the value obtained by multiplying the mass thereof withthe Avogadro's number becomes the functional group equivalent (g/mol).

When two or more monomers, each having a functional group equivalentdifferent from those of the others and having a polyorganosiloxaneskeleton, are used, the arithmetic mean value of the functional groupequivalents can be used as the functional group equivalent of themonomers. That is, the functional group equivalent of the monomers canbe calculated from the following equation: Functional group equivalentof monomer mixture (g/mol)=(Functional group equivalent of monomer1×Blend amount of monomer 1+ . . . Functional group equivalent ofmonomer 2×Blend amount of monomer 2+ . . . Functional group equivalentof monomer n×Blend amount of monomer n)/(Blending amount of monomer1+Blending amount of monomer 2+ . . . +Blending amount of monomer n)

The content of the monomer (B1) based on the mass of the total monomercomponents of the polymer (B) can be, for instance, 0.5% by mass ormore, 1% by mass or more, 3% by mass or more, or even 4.5% by mass ormore. In some embodiments, from the standpoint of suppressing thepressure-sensitive adhesive force at the beginning of attachment moreeffectively, the content of the monomer (B1) can be 5% by mass or more,10% by mass or more, 15% by mass or more, or even 20% by mass or more.Although the content of the monomer (B1) based on the mass of the totalmonomer components of the polymer (B) can be 100% by mass, in view ofthe polymerization reactivity and compatibility, it may be normallypreferably 80% by mass or less, 60% by mass or less, 50% by mass orless, 40% by mass or less, or even 30% by mass or less. In someembodiments, from the standpoint of facilitating to obtain apressure-sensitive adhesive sheet favorably combining the lowpressure-sensitive adhesive force at the beginning of attachment with anincrease in pressure-sensitive adhesive force occurring over time, thecontent of the monomer (B1) can be 5% by mass or more but 50% by mass orless, preferably 10% by mass or more but 40% by mass or less, and morepreferably 15% by mass or more but 30% by mass or less, based on themass of the total monomer components of the polymer (B).

The monomer components for preparing the polymer (B) may contain amonomer (B2) whose homopolymer has a glass transition temperature of 40C.° or higher, in addition to the monomer having a polyorganosiloxaneskeleton described above. With the use of monomer (B2) whose homopolymerhas a glass transition temperature of 40 C.° or higher in the polymer(B), pressure-sensitive adhesive force occurring at the beginning ofattachment can be favorably suppressed and pressure-sensitive adhesiveforce can be suitably increased over time. In some embodiments, for themonomer (B2), a monomer whose homopolymer has a glass transitiontemperature of 60 C.° or higher can be preferably used. For instance, amonomer whose homopolymer has a glass transition temperature of 70 C.°or higher (preferably 80 C.° or higher, more preferably 90 C.° orhigher, for instance, 100 C.° or higher) can be suitably used as themonomer (B2). For the monomer (B2), a monomer whose homopolymer has aglass transition temperature the satisfies any one or more conditionsdescribed herein can be used. For instance, (meth)acrylic monomers suchas (meth)acrylic acid alkyl ester and (meth) acrylic acid ester havingan alicyclic hydrocarbon group at an ester end can be used as a monomer(B2), although not limited thereto. Examples of monomers usable asmonomer (B2) include (meth)acrylic monomers, such as, for example,dicyclopentanyl methacrylate (Tg: 175C.°, dicyclopentanyl acrylate (Tg:120C.°), isobornyl methacrylate (Tg: 173C.°), isobornyl acrylate (Tg:97) C.°, methyl methacrylate (Tg: 105C.°), 1-adamantyl methacrylate (Tg:250C.°), and 1-adamantyl acrylate (Tg: 153C.°).

The polymer (B) may be a copolymer of the aforementioned (meth)acrylicmonomer and the following monomer (however, the glass transitiontemperature of the homopolymer thereof is 40° C. or higher). Examples ofthe monomer copolymerizable with the aforementioned (meth)acrylicmonomer include: amide group-containing vinyl monomers, such as acryloylmorpholine (Tg: 145° C.), dimethylacrylamide (Tg: 119° C.),diethylacrylamide (Tg: 81° C.), dimethylaminopropylacrylamide (Tg: 134°C.), isopropylacrylamide (Tg: 134° C.), and hydroxyethyl acrylamide (Tg:98° C.); and lactam monomers, such as N-vinyl caprolactams includingN-vinyl-2-caprolactam, etc.

The content of the monomer (B2) whose homopolymer has a glass transitiontemperature of 40 C.° or higher is not particularly limited to aspecific range and can be selected so that the desired effect with theuse of the monomer (B1) may preferably be obtained. In some embodiment,from the standpoint of facilitating to obtain a pressure-sensitiveadhesive sheet favorably combining the low pressure-sensitive adhesiveforce at the beginning of attachment with an increase inpressure-sensitive adhesive force occurring over time, the content ofthe monomer (B2) based on the mass of the total monomer components ofthe polymer (B) can be, for instance, 10% by mass or more, preferably20% by mass or more, and more preferably 30% is by mass or more. In someembodiments, the content of the monomer (B2) based on the mass of thetotal monomer components of the polymer (B) can be, for instance, 80% bymass or less, preferably 60% by mass or less, and more preferably 50% bymass or less, based on the mass of the total monomer components of thepolymer (B).

The monomer components for preparing the polymer (B) may contain amonomer (for instance, a (meth)acrylic monomer) whose homopolymer has aglass transition temperature lower than 80 C.° (for instance, −20 C.° orhigher, but lower than 80C.°). Examples of the (meth)acrylic monomerwhose homopolymer has a glass transition temperature lower than 80 C.°include, for example, n-butyl methacrylate (Tg: 20C.°) and 2-ethylhexylmethacrylate (Tg: −10C.°), etc. In some embodiments, the monomercomponents for preparing the polymer (B) may contain a monomer whosehomopolymer has a glass transition temperature lower than 80 C.° (forinstance, lower than 60 C.°, or even lower than 40C.°) and a monomerwhose homopolymer has a glass transition temperature of 80 C.° or higher(for instance, 90 C.° or higher, or even 100 C.° or higher) incombination. This facilitates obtaining a pressure-sensitive adhesivesheet that may exhibit, after an increase in pressure-sensitive adhesiveforce occurring over time, favorable pressure-sensitive adhesive forceand cohesive force in a well-balanced manner.

The polymer (B) may be a copolymer containing the monomer having apolyorganosiloxane skeleton, optionally containing the monomer (forinstance, the (meth)acrylic monomer) is whose homopolymer has a glasstransition temperature of 40 C.° or higher, and further containing oneor more monomers selected from the group consisting of a (meth)acrylicmonomer having an alicyclic structure, a monomer having apolyoxyalkylene skeleton, a (meth)acrylic acid ester monomer, and acopolymerizable monomer.

Examples of such a (meth)acrylic acid ester monomer include:(meth)acrylic acid alkyl esters, such as (meth)acrylic acid methyl,(meth)acrylic acid ethyl, (meth)acrylic acid propyl, (meth)acrylic acidisopropyl, (meth)acrylic acid butyl, (meth)acrylic acid isobutyl,(meth)acrylic acid s-butyl, (meth)acrylic acid t-butyl, (meth)acrylicacid pentyl, (meth)acrylic acid isopentyl, (meth)acrylic acid hexyl,(meth)acrylic acid-2-ethylhexyl, (meth)acrylic acid heptyl,(meth)acrylic acid octyl, (meth)acrylic acid isooctyl, (meth)acrylicacid nonyl, (meth)acrylic acid isononyl, (meth)acrylic acid decyl,(meth)acrylic acid isodecyl, (meth)acrylic acid undecyl, and(meth)acrylic acid dodecyl; (meth)acrylic acid aryl esters, such as(meth)acrylic acid phenyl and (meth)acrylic acid benzyl; (meth)acrylicacid esters obtained from terpene compound derivative alcohols; and thelike. These (meth)acrylic acid esters can be used alone or incombination of two or more thereof.

The polymer (B) can also be obtained by copolymerizing, other than the(meth)acrylic acid ester component unit, another monomer component(copolymerizable monomer) copolymerizable with the (meth)acrylic acidester. For example, a functional group that is reactive with an epoxygroup or an isocyanate group may be introduced into the polymer (B).Examples of such a functional group include a hydroxyl group, carboxylgroup, amino group, amide group, and mercapt group, and a monomer havingsuch a functional group may be used (copolymerized) in producing thepolymer (B).

Examples of the another monomer that is copolymerizable with the(meth)acrylic acid ester include: carboxyl group-containing monomers,such as acrylic acid, methacrylic acid, carboxy ethyl acrylate,carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid,crotonic acid, and isocrotonic acid; (meth)acrylic acid alkoxy alkylmonomers, such as (meth)acrylic acid methoxyethyl, (meth)acrylic acidethoxyethyl, (meth)acrylic acid propoxyethyl, (meth)acrylic acidbutoxyethyl, and (meth)acrylic acid ethoxypropyl; salts, such as(meth)acrylic acid alkali metal salt; di(meth)acrylic acid estermonomers of (poly)oxyalkylene, such as di(meth)acrylic acid ester ofethylene glycol, di(meth)acrylic acid ester of diethylene glycol,di(meth)acrylic acid ester of triethylene glycol, di(meth)acrylic acidester of polyethylene glycol, di(meth)acrylic acid ester of propyleneglycol, di(meth)acrylic acid ester of dipropylene glycol, anddi(meth)acrylic acid ester of tripropylene glycol; poly(meth)acrylicacid ester monomers, such as trimethylolpropane tri(meth)acrylic acidester; vinyl esters, such as vinyl acetate and vinyl propionate;halogenated vinyl compounds, such as vinylidene chloride and(meth)acrylic acid-2-chloroethyl; oxazoline group-containingpolymerizable compounds, such as 2-vinyl-2-oxazoline,2-vinyl-5-methyl-2-oxazoline, and 2-isopropenyl-2-oxazoline; aziridinegroup-containing polymerizable compounds, such as(meth)acryloylaziridine and (meth)acrylic acid-2-aziridinylethyl; epoxygroup-containing vinyl monomers, such as allyl glycidyl ether,(meth)acrylic acid glycidyl ether, and (meth)acrylic acid-2-ethylglycidyl ether; hydroxyl group-containing vinyl monomers, such as(meth)acrylic acid-2-hydroxyethyl, (meth)acrylic acid-2-hydroxypropyl,and adducts between lactones and (meth)acrylic acid-2-hydroxyethyl;

fluorine-containing vinyl monomers, such as fluorine-substituted(meth)acrylic acid alkyl ester; acid anhydride group-containingmonomers, such as maleic acid anhydride and itaconic acid anhydride;aromatic vinyl compound monomers, such as styrene, α-methylstyrene, andvinyl toluene; reactive halogen-containing vinyl monomers, such as2-chloroethyl vinyl ether and monochloro vinyl acetate; amidegroup-containing vinyl monomers, such as (meth)acrylamide,N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide,N,N-diethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,N-methylol(meth)acrylamide, N-ethylol(meth)acrylamide,N-methylolpropane(meth)acrylamide, N-methoxyethyl(meth)acrylamide,N-butoxymethyl(meth)acrylamide, and N-acryloyl morpholine; succinimidemonomers, such as N-(meth)acryloyloxy methylene succinimide,N-(meth)acryloyl-6-oxy hexamethylene succinimide, andN-(meth)acryloyl-8-oxy hexamethylene succinimide; maleimide monomers,such as N-cyclohexyl maleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenyl maleimide; itaconimide monomers, such asN-methylitaconimide, N-ethylitaconimide, N-butylitaconimide,N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide,and N-laurylitaconimide; nitrogen-containing heterocyclic monomers, suchas N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine,N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine,N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole,N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine,N-(meth)acryloylpyrrolidine, N-vinyl morpholine, N-vinyl pyrazole,N-vinyl isoxazole, N-vinyl thiazole, N-vinyl isothiazole, and N-vinylpyridazine; N-vinyl carboxylic acid amides; lactam monomers, such asN-vinyl caprolactam; cyanoacrylate monomers, such as(meth)acrylonitrile; (meth)acrylic acid aminoalkyl monomers, such as(meth)acrylic acid aminoethyl, (meth)acrylic acidN,N-dimethylaminoethyl, (meth)acrylic acid N,N-dimethylaminoethyl, and(meth)acrylic acid t-butylaminoethyl; imide group-containing monomers,such as cyclohexyl maleimide and isopropyl maleimide; isocyanategroup-containing monomers, such as 2-isocyanate ethyl(meth)acrylate;organic silicon-containing vinyl monomers, such asvinyltrimethoxysilane, γ-methacryloxpropyl trimethoxy silane,allyltrimethoxysilane, trimethoxysilylpropylallylamine, and 2-methoxyethoxy trimethoxy silane; hydroxyl group-containing monomers, such as(meth)acrylic acid hydroxyalkyls including (meth)acrylic acidhydroxyethyl, (meth)acrylic acid hydroxypropyl, (meth)acrylic acidhydroxybutyl, (meth)acrylic acid hydroxyhexyl, (meth)acrylic acidhydroxyoctyl, (meth)acrylic acid hydroxydecyl, (meth)acrylic acidhydroxy lauryl, and (4-hydroxymethyl cyclohexyl)methyl methacrylate;acrylic acid ester monomers having a heterocycle, halogen atom, siliconatom, or the like, such as (meth)acrylic acid tetrahydrofurfuryl,fluorine atom-containing (meth)acrylate, and silicone(meth)acrylate;olefin monomers, such as isoprene, butadiene, and isobutylene; vinylether monomers, such as methyl vinyl ether and ethyl vinyl ether;olefins or dienes, such as ethylene, butadiene, isoprene, andisobutylene; vinyl ethers, such as vinyl alkyl ether; vinyl chloride;and others, such as macromonomers having a radically polymerizable vinylgroup at the monomer end to which a vinyl group has been polymerized,etc. These monomers can be copolymerized, alone or in combinationthereof, with the (meth)acrylic acid esters.

In the polymer (B), the content of other monomer components, other thanthe monomer (B1) having a polyorganosiloxane skeleton and the monomer(B2) whose homopolymer has a glass transition temperature of 40 C.° orhigher, is preferably 0% by mass or more but 85% by mass or less, morepreferably 0% by mass or more but 70% by mass or less, and still morepreferably 20% by mass or more but 55% by mass or less, based on themass of the total monomer components of the polymer (B).

In some embodiments, the polymer (B) is preferably the polymer havingsubstantially no functional group which causes a crosslinking reactionwith the polymer (A). In other words, in such embodiments, the polymer(B) is preferably contained in the pressure-sensitive adhesive layerwithout chemically bonded to the polymer (A). The pressure-sensitiveadhesive layer containing the polymer (B) in such a form is suitable toexhibit both the low pressure-sensitive adhesive force at the beginningof attachment and an increase in pressure-sensitive adhesive forceoccurring over time, due to the good mobility of the polymer (B). Thefunctional group which causes a crosslinking reaction with the polymer(A) may vary depending on the type of the functional group in thepolymer (A), but may be, for example, an epoxy group, an isocyanategroup, a carboxy group, an alkoxysilyl group.

The weight average molecular weight (MwB) of the polymer (B) is notparticularly limited and can be selected so that the desired effect withthe use of the polymer (B) may preferably be obtained. The weightaverage molecular weight (MwB) can be, for instance, 1000 or more, or5000 or more. From the standpoint of favorably combining the lowpressure-sensitive adhesive force at the beginning of attachment with anincrease in pressure-sensitive adhesive force occurring over time, insome embodiments, the MwB can be, for instance, 10000 or more, 12000 ormore, 15000 or more, and even 20000 or more. In some embodiments, theMwB can be 50000 or more, 80000 or more, 100000 or more, or even 120000or more (for instance, 150000 or more). The MwB can be, for instance,500000 or less, 350000 or less, 250000 or less, 150000 or less, or even100000 or less. From the standpoint of the ease of sufficientlysuppressing the pressure-sensitive adhesive force at the beginning ofthe attachment, in some embodiments, the MwB can be less than 100000,less than 80000, less than 70000, less than 50000, less than 40000, lessthan 20000, or even less than 10000.

The weight average molecular weights of the polymer (A) and the polymer(B) can be determined by a gel permeation chromatography (GPC) methodand by polystyrene conversion. Specifically, the measurement isperformed in accordance with the method and conditions described in thelater-described Examples.

The polymer (B) can be produced by polymerizing the aforementionedmonomers with, for example, a solution polymerization method, bulkpolymerization method, emulsion polymerization method, suspensionpolymerization, block polymerization, or the like.

In order to adjust the molecular weight of the polymer (B), a chaintransfer agent can be used during the polymerization. Examples of thechain transfer agent to be used include: compounds having a mercaptgroup, such as octylmercaptan, laurylmercaptan, t-nonyl mercaptan,t-dodecyl mercaptan, mercaptoethanol, and α-thioglycerol; thioglycolicacid, methyl thioglycolate, ethyl thioglycolate, propyl thioglycolate,butyl thioglycolate, t-butyl thioglycolate, 2-ethylhexyl thioglycolate,octyl thioglycolate, isooctyl thioglycolate, decyl thioglycolate,dodecyl thioglycolate, and thioglycolic acid esters includingthioglycolic acid ester of ethylene glycol, thioglycolic acid ester ofneopentyl glycol, and thioglycolic acid ester of pentaerythritol;α-methylstyrene dimer; and the like.

The use amount of the chain transfer agent is not particularly limited,but is contained in an amount of usually 0.05 parts by mass to 20 partsby mass, preferably 0.1 parts by mass to 15 parts by mass, and morepreferably 0.2 parts by mass to 10 parts by mass, based on 100 parts bymass of the monomer. By thus adjusting the addition amount of the chaintransfer agent, the (meth)acrylic polymer (B) having a preferredmolecular weight can be obtained. The chain transfer agents can be usedalone or in combination of two or more thereof.

[Pressure-Sensitive Adhesive Composition]

The pressure-sensitive adhesive composition includes the aforementionedpolymer (A) and the polymer (B). The content of the polymer (B) relativeto the content of the polymer (A) can be selected so that both the lowpressure-sensitive adhesive force at the beginning of attachment and anincrease in pressure-sensitive adhesive force occurring over time mayfavorably obtained. In some embodiments, the content of the polymer (B)based on 100 parts by mass of the polymer (A) can be, for instance, 0.1part by mass or more, 0.3 part by mass or more, 0.4 part by mass ormore, 0.5 part by mass or more, 1 past by mass or more,

or even 2 parts by mass or more. In some embodiments, from thestandpoint of reworkability, the content of the polymer (B) can be 3parts by mass or more, 4 parts by mass or more, or even 5 parts by massor more. The content of the polymer (B) based on 100 parts by mass ofthe polymer (A) can be, for instance, 75 parts by mass or less, 60 partsby mass or less, or even 50 parts by mass or less. From the standpointof avoiding the cohesiveness in the pressure-sensitive adhesive layerbeing excessively low, in some embodiments the content of the polymer(B) based on 100 parts by mass of the polymer (A) can be, for instance,40 parts by mass or less, 35 parts by mass or less, 30 parts by mass orless, or even 25 parts by mass or less. In some embodiments, from thestandpoint of obtaining a pressure-sensitive adhesive sheet exhibitinghigher pressure-sensitive adhesive force after an increase in occurringover time, the content of the polymer (B) based on 100 parts by mass ofthe polymer (A) can be 20 parts by mass or less, 17 parts by mass orless, 15 parts by mass or less, 12 parts by mass or less, 10 parts bymass or less, 8 parts by mass or less, 6 parts by mass or less, or even4 parts by mass or less (for instance, 3 parts by mass or less).

The pressure-sensitive adhesive composition may contain, other than theaforementioned polymer (A) and polymer (B), various types of additivesthat are common in the field of pressure-sensitive adhesivecompositions, as optional components. Such optional components areexemplified by a tackifying resin, cross-linking agent, catalyst,plasticizer, softener, filler, colorant (pigment, dye, or the like),antioxidant, leveling agent, stabilizer, antiseptic, and antistaticagent, etc. Such additives that are conventionally and publicly knowncan be used by ordinary methods.

In order to adjust the cohesive force of the later-describedpressure-sensitive adhesive layer, a cross-linking agent can also beused other than the aforementioned various monomers. Commonly-usedcross-linking agents can be used as the cross-linking agent. Examples ofthe cross-linking agents include, for example, an epoxy cross-linkingagent, isocyanate cross-linking agent, silicone cross-linking agent,oxazoline cross-linking agent, aziridine cross-linking agent, silanecross-linking gent, alkyl-etherified melamine cross-linking agent, andmetal chelate cross-linking agent, etc. In particular, an isocyanatecross-linking agent, epoxy cross-linking agent, and metal chelatecross-linking agent can be preferably used. These compounds may be usedalone or in combination of two or more thereof.

Specific examples of the isocyanate cross-linking agent include tolylenediisocyanate, hexamethylene diisocyanate, isophorone diisocyanate,xylylene diisocyanate, hydrogenated xylylene diisocyanate,diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate,tetramethyl xylylene diisocyanate, naphthalene diisocyanate,triphenylmethane triisocyanate, polymethylene polyphenyl isocyanate, andadducts of these compounds with polyols such as trimethylolpropane.Additionally, a compound having, in one molecule, at least oneisocyanate group and one or more unsaturated bonds, specifically2-isocyanate ethyl(meth)acrylate, etc., can also be used as theisocyanate cross-linking agent. These compounds may be used alone or incombination of two or more thereof.

Examples of the epoxy cross-linking agent include, bisphenol A,epichlorohydrin type epoxy resin, ethyleneglycidylether, polyethyleneglycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidylether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidylether, diglycidyl aniline, diamine glycidyl amine,N,N,N′,N′-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl) cyclohexane, etc. These compounds may be used alone or incombination of two or more thereof.

Examples of the metal chelate compound include: as metal components,aluminum, iron, tin, titanium, and nickel; and as chelate components,acetylene, methyl acetoacetate, and ethyl lactate, etc. These compoundsmay be used alone or in combination of two or more thereof.

When using a crosslinking agent, its amount used is not particularlylimited. For instance, its amount can be greater than 0 part by massrelative to 100 parts by mass of the polymer (A). The amount ofcrosslinking agent used to 100 parts by mass of the polymer (A) can be,for instance, 0.01 part by mass or greater, or preferably 0.05 part bymass or greater. With increasing amount of crosslinking agent used, thepressure-sensitive adhesive force at the beginning of attachment tendsto be lower and the reworkability tends to be improved. In someembodiments, the amount of crosslinking agent used to 100 parts by massof the polymer (A) can be 0.1 part by mass or greater, 0.5 part by massor greater, or even 0.8 part by mass or greater.

On the other hand, from the standpoint of allowing the adequate mobility(migration) of the polymer (B) in the pressure-adhesive layer tofacilitate an increase in pressure-sensitive adhesive force occurringover time, the amount of crosslinking agent used to 100 parts by mass ofthe polymer (A) is usually suitably 15 parts by mass or less, 10 partsby mass or less, or even 5 parts by mass or less.

In some embodiments, from the standpoint of obtaining apressure-sensitive adhesive sheet favorably combining adequate cohesiveforce with an increase in pressure-sensitive adhesive force occurringover time, the cross-linking agent is preferably contained, in an amountof 0.01 parts by mass to 15 parts by mass, and more preferably containedin an amount of 0.5 parts by mass to 10 parts by mass, based on 100parts by mass of the polymer (A).

In some embodiments, at least an isocyanate-based crosslinking agent canbe used as the crosslinking agent. From the standpoint of obtaining apressure-sensitive adhesive sheet favorably combining the lowpressure-sensitive adhesive force at the beginning of attachment with anincrease in pressure-sensitive adhesive force occurring over time, insome embodiments, the amount of the isocyanate-based crosslinking agentused to 100 parts by mass of the polymer (A) can be, for instance, 0.01parts by mass or more, 0.1 parts by mass or more, 0.3 parts by mass ormore, or even 0.5 parts by mass or more, and it can be, for instance, 5parts by mass or less, 4 parts by mass or less, or even 3 parts by massor less.

The pressure-sensitive adhesive composition disclosed herein may furtherinclude a cross-linking catalyst for further effectively promoting anyone of the aforementioned cross-linking reactions. As such across-linking catalyst, for example, a tin catalyst (in particular,dioctyl tin dilaurate) can be preferably used. The use amount of thecross-linking catalyst (e.g., a tin catalyst such as dioctyl tindilaurate) is not particularly limited, but the use amount may be, forexample, approximately 0.0001 parts by mass to 1 part by mass, based on100 parts by mass of the polymer (A).

The tackifying resin is not particularly limited. Examples thereofinclude, for example, a rosin tackifying resin, terpene tackifyingresin, phenol tackifying resin, hydrocarbon tackifying resin, ketonetackifying resin, polyamide tackifying resin, epoxy tackifying resin,and elastomer tackifying resin, etc.

Examples of the rosin tackifying resin include, for example, unmodifiedrosin (raw rosin), such as gum rosin, wood rosin, and tall oil rosin;modified rosins obtained by modifying these unmodified rosin withpolymerization, disproportionation, and hydrogenation, etc. (polymerizedrosin, stabilized rosin, disproportionated rosin, completelyhydrogenated rosin, partially hydrogenated rosin, and chemicallymodified other rosin, etc.); and various rosin derivatives. Examples ofthe rosin derivatives include, for example: rosin phenol resins obtainedby adding phenol to rosins (unmodified rosin, modified rosin, andvarious rosin derivatives, etc.) with an acid catalyst followed by beingsubjected to thermal polymerization; rosin ester resins, such as rosinester compounds (unmodified rosin esters) obtained by esterifyingunmodified rosin with alcohols, and modified rosin ester compounds (suchas polymerized rosin ester, stabilized rosin ester, disproportionatedrosin ester, completely hydrogenated rosin ester, and partiallyhydrogenated rosin ester) obtained by esterifying modified rosin (suchas polymerized rosin, stabilized rosin, disproportionated rosin,completely hydrogenated rosin, and partially hydrogenated rosin) withalcohols; unsaturated fatty acid-modified rosin resins obtained bymodifying unmodified rosin or modified rosin (polymerized rosin,stabilized rosin, disproportionated rosin, completely hydrogenatedrosin, and partially hydrogenated rosin, etc.) with an unsaturated fattyacid; unsaturated fatty acid-modified rosin ester resins obtained bymodifying rosin ester resins with an unsaturated fatty acid; rosinalcohol resins obtained by subjecting carboxyl groups in unmodifiedrosin, modified rosin (polymerized rosin, stabilized rosin,disproportionated rosin, completely hydrogenated rosin, and partiallyhydrogenated rosin, etc.), unsaturated fatty acid-modified rosin resins,or unsaturated fatty acid-modified rosin esters to a reductiontreatment; metal salts of rosin resins (in particular, rosin esterresins), such as unmodified rosin, modified rosin, and various rosinderivatives; and the like.

Examples of the terpene tackifying resin include, for example: terpeneresins, such as an α-pinene polymer, β-pinene polymer, and dipentenepolymer; modified terpene resins obtained by modifying (phenolmodification, aromatic modification, hydrogenation modification, andhydrocarbon modification, etc.) these terpene resins (e.g., a terpenephenol resin, styrene modified terpene resin, aromatic modified terpeneresin, and hydrogenated terpene resin, etc.); and the like.

Examples of the phenol tackifying resin include, for example:condensates of various phenols (e.g., phenol, m-cresol, 3,5-xylenol,p-alkylphenol, and resorcinol, etc.) and formaldehydes (e.g., analkylphenol resin and xyleneformaldehyde resin, etc.); resols obtainedby subjecting the phenols and the formaldehydes to an addition reactionwith an alkali catalyst; novolacs obtained by subjecting the phenols andthe formaldehydes to a condensation reaction with an acid catalyst; andthe like.

Examples of the hydrocarbon tackifying resin (petroleum tackifyingresin) include, for example: aliphatic hydrocarbon resins [polymers ofaliphatic hydrocarbons, such as C₄₋₅ olefins and dienes (olefins such asbutene-1, isobutylene, and pentene-1; and dienes such as butadiene,1,3-pentadiene, and isoprene)]; aliphatic cyclic hydrocarbon resins[alicyclic hydrocarbon resins obtained by subjecting a so-called “C₄petroleum fraction” or “C₅ petroleum fraction” tocyclization/dimerization followed by being subjected to polymerization;polymers of cyclic diene compounds (cyclopentadiene, dicyclopentadiene,ethylidene norbornene, and dipentene, etc.) or hydrogenated compoundsthereof; and alicyclic hydrocarbon resins obtained by hydrogenating thearomatic ring of the following aromatic hydrocarbon resins and aliphaticand aromatic petroleum resins]; aromatic hydrocarbon resins [polymers ofC₈₋₁₀ vinyl group-containing aromatic hydrocarbons (styrene, vinyltoluene, α-methylstyrene, indene, and methylindene, etc.)]; aliphaticand aromatic petroleum resins (styrene-olefin copolymers, etc.);aliphatic and alicycle petroleum resins; hydrogenated hydrocarbonresins; cumarone resins; cumarone indene resins; and the like.

Commercially available products of the polymerized rosin ester that canbe preferably used are exemplified by the products with the names of“PENSEL D-125”, “PENSEL D-135”, “PENSEL D-160”, “PENSEL KK”, and “PENSELC”, etc., which are all made by ARAKAWA CHEMICAL INDUSTRIES, LTD., butare not limited thereto.

Commercially available products of the terpene phenol resin that can bepreferably used are exemplified by the products: with the names of “YSPolystar S-145” “YS Polystar G-125”, “YS Polystar N125”, “YS PolystarU-115”, which are made by YASUHARA CHEMICAL CO., LTD.; with the names of“TAMANOL 803L” and “TAMANOL 901”, which are made by ARAKAWA CHEMICALINDUSTRIES, LTD.; with the name of “SUMILITE RESIN PR-12603” made bySUMITOMO BAKELITE CO., LTD.; and the like; but are not limited thereto.

[Pressure-Sensitive Adhesive Layer and Pressure-Sensitive AdhesiveSheet]

Subsequently, the structure of a pressure-sensitive adhesive sheet,having a pressure-sensitive adhesive layer including apressure-sensitive adhesive composition having the aforementionedcomposition, will be described.

The pressure-sensitive adhesive layer can be a layer in which apressure-sensitive adhesive composition has been cured. That is, thepressure-sensitive adhesive layer can be formed by providing thepressure-sensitive adhesive composition to an appropriate supportingbody (e.g., application, coating) and then by appropriately subjectingit to a curing treatment. When two or more types of curing treatments(drying, cross-link formation, polymerization, etc.) are performed,these treatments can be performed simultaneously or in multiple stages.In the case of the pressure-sensitive adhesive composition using apartial polymer (acrylic polymer syrup), a final copolymerizationreaction is typically performed as the curing treatment (the partialpolymer is subjected to a further copolymerization reaction to form acomplete polymer). For example, in the case of a photo-curingpressure-sensitive adhesive composition, light irradiation is performed.A curing treatment, such as cross-link formation, drying, or the like,may be performed, if necessary. For example, when a photo-curingpressure-sensitive adhesive composition needs to be dried, photo-curingmay be performed after the drying of the composition. In the case of apressure-sensitive adhesive composition using a complete polymer, atreatment, such as drying (drying by heating), cross-link formation, orthe like, is typically performed as the curing treatment, if necessary.

The application/coating of the pressure-sensitive adhesive compositioncan be performed by using a commonly-used coater, such as, for example,a gravure roll coater, reverse roll coater, kiss roll coater, dip rollcoater, bar coater, knife coater, spray coater, or the like.Alternatively, the pressure-sensitive adhesive layer may be formed bydirectly providing the pressure-sensitive adhesive composition to asupporting body, or the pressure-sensitive adhesive layer formed on arelease liner may be transferred to a supporting body.

The ratio of a solvent-insoluble component in the pressure-sensitiveadhesive layer is not particularly limited. The ratio of asolvent-insoluble component can be, for instance, within a range of20.0% by mass to 99.0% by mass, and normally suitably within a range of30.0% by mass to 90.0% by mass. From the standpoint of obtaining apressure-sensitive adhesive sheet favorably combining adequate cohesiveforce with an increase in pressure-sensitive adhesive force occurringover time, in some embodiments, the ratio of a solvent-insolublecomponent in the pressure-sensitive adhesive layer can be within a rangeof 55.0% by mass to 99.0% by mass, and preferably within a range of60.0% by mass to 95.0% by mass. A method of evaluating the ratio of asolvent-insoluble component will be described later.

The thickness of the pressure-sensitive adhesive layer is notparticularly limited, and can be, for instance, 1 μm or larger. In someembodiments, the thickness of the pressure-sensitive adhesive layer maybe, for instance, usually 3 μm or larger, 5 μm or larger, 8 μm orlarger, 10 μm or larger, 15 μm or larger, or even 20 μm or larger orlarger than 20 μm. With the increase in thickness of thepressure-sensitive adhesive layer, the pressure-sensitive adhesive forceobserved after an increase in pressure-sensitive adhesive forceoccurring over time tends to be greater. In some embodiments, thethickness of the pressure-sensitive adhesive layer can be, for instance,300 μm or less, 200 μm or less, 150 μm or less, 100 μm or less, 70 μm orless, 50 μm or less, or even 40 μm or less. From the standpoint ofreducing the total thickness of the pressure-sensitive adhesive sheetand/or avoiding the occurrence of cohesive failure in thepressure-sensitive adhesive layer, it may be advantageous that thethickness of the pressure-sensitive adhesive layer is not excessivelylarge.

The pressure-sensitive adhesive sheet according to the presentembodiment comprises a pressure-sensitive adhesive layer made of thepressure-sensitive adhesive composition. The pressure-sensitive adhesivesheet disclosed herein may be in a form that a pressure-sensitiveadhesive layer is provided on at least one surface of a supporting bodyin a fixed manner, i.e., without an intention of separating thepressure-sensitive adhesive layer from the supporting body, or in a formwithout a supporting body fixed to the pressure-sensitive adhesive layerand typically formed solely of the pressure-sensitive adhesive layer (asupporting body-free pressure-sensitive adhesive sheet).

In case that the pressure-sensitive adhesive sheet disclosed herein isin a form of a double-faced pressure-sensitive adhesive sheet having afirst pressure-sensitive adhesive layer on a first side of thesupporting body and a second pressure-sensitive adhesive layer on asecond side of the supporting body, the aforementionedpressure-sensitive adhesive layer's thickness can be applied to at leastthe thickness of the first pressure-sensitive adhesive layer. Thethickness of the second pressure-sensitive adhesive layer may also beselected from the aforementioned pressure-sensitive adhesive layer'sthickness. In case of a supporting body-free pressure-sensitive adhesivesheet formed of a pressure-sensitive adhesive layer, thepressure-sensitive adhesive layer's thickness is equal to thepressure-sensitive adhesive sheet's thickness.

The concept of the pressure-sensitive adhesive sheet described hereincan involve objects referred to as a pressure-sensitive adhesive tape, apressure-sensitive adhesive film, and a pressure-sensitive adhesivelabel, etc. The pressure-sensitive adhesive sheet may be one cut orpunched into an appropriate shape in accordance with its purpose of use.The pressure-sensitive adhesive layer is not limited to one continuouslyformed, but may be one formed into a regular pattern, such as, forexample, a dot shape and a stripe shape, or formed into a randompattern.

The aforementioned supporting body can be formed of a materialappropriately selected, in accordance with the application of thepressure-sensitive adhesive tape, from the group consisting of, forexample: plastic films, such as polyolefin films including polyethylene,polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylenepropylene copolymer, ethylene 1-butene copolymer, ethylene vinyl acetatecopolymer, ethylene ethyl acrylate copolymer, and ethylene vinyl alcoholcopolymer, polyester films including polyethylene terephthalate,polyethylene naphthalate, and polybutylene terephthalate, polyacrylatefilm, polystyrene film, polyamide films including nylon 6, nylon 6,6,and partially aromatic polyamide, polyvinylchloride film, polyvinylidenechloride film, and polycarbonate film; foam substrates, such as apolyurethane foam, and polyethylene foam; paper, such as craft paper,crepe paper, and Japanese paper; cloth, such as cotton cloth and staplefiber cloth; nonwoven cloth, such as polyester nonwoven cloth andvinylon nonwoven cloth; metallic foils, such as aluminum foil and copperfoil; and the like.

The supporting body can also be subjected to, if necessary: amold-release and antifouling treatment using a release agent, such as asilicone release agent, fluorine release agent, long-chain alkyl releaseagent, or fatty acid amide release agent, and a silica powder; and aneasy-adhesion treatment, such as an acid treatment, alkali treatment,primer treatment, corona treatment, plasma treatment, ultraviolettreatment, or the like. The thickness of the supporting body can beappropriately selected in accordance with its purpose, but is generallywithin a range of approximately 5 μm to 200 μm (typically within a rangeof 10 μm to 100 μm).

The supporting body can also be subjected to, if necessary: amold-release and antifouling treatment using a release agent, such as asilicone release agent, fluorine release agent, long-chain alkyl releaseagent, or fatty acid amide release agent, and a silica powder; aneasy-adhesion treatment, such as an acid treatment, alkali treatment,primer treatment, corona treatment, plasma treatment, ultraviolettreatment, or the like; and an antistatic treatment, such as a coatingtype, kneading type, vapor deposition type, or the like.

In order to protect a pressure-sensitive adhesive surface, a releaseliner can be attached, if necessary, to the surface of thepressure-sensitive adhesive layer in the pressure-sensitive adhesivesheet of the present embodiment.

Paper or a plastic film can be used as a material for forming therelease liner, but a plastic film is preferably used because it isexcellent in surface smoothness. The film is not particularly limited,as far as it can protect the pressure-sensitive adhesive layer. Examplesof the film include, for example, a polyethylene film, polypropylenefilm, polybutene film, polybutadiene film, polymethylpentene film,polyvinylchloride film, vinylchloride copolymer film, polyethyleneterephthalate film, polybutylene terephthalate film, polyurethane film,and ethylene-vinylacetate copolymer film, etc.

The thickness of the release liner is usually within a range of 5 μm to200 μm, and preferably within a range of approximately 10 μm to 100 μm.When the thickness is within the aforementioned range, the release lineris excellent in the workability for attaching to the pressure-sensitiveadhesive layer and the workability for releasing therefrom, and hencethe release liner is preferred. The release liner can also be subjectedto, if necessary: a mold-release and antifouling treatment using arelease agent, such as a silicone release agent, fluorine release agent,long-chain alkyl release agent, or fatty acid amide release agent, and asilica powder; and an antistatic treatment, such as an coating type,kneading type, vapor is deposition type, or the like.

The pressure-sensitive adhesive sheet has the characteristics that: thepressure-sensitive adhesive force thereof is small immediately afterbeing attached to an adherend, and hence rework can be performed; thepressure-sensitive adhesive force is increased over time; and theadhesion reliability is high. The pressure-sensitive adhesive force,occurring immediately after the pressure-sensitive adhesive sheet isattached (after 30 minutes at room temperature), can be evaluated by a180°-peeling pressure-sensitive adhesive force test performed under theconditions in which a tensile speed is 300 mm/min and a peeling angle is180°. The 180°-peeling pressure-sensitive adhesive force test isperformed in accordance with the method and conditions described in thelater-described Examples.

Additionally, the pressure-sensitive adhesive force of thepressure-sensitive adhesive sheet, occurring over time, can be evaluatedby a 180°-peeling pressure-sensitive adhesive force test performed underthe conditions in which a tensile speed is 300 mm/min and a peelingangle is 180°. The 180°-peeling pressure-sensitive adhesive force testis performed in accordance with the method and conditions described inthe later-described Examples.

Further, the pressure-sensitive adhesive sheet has a characteristic thatcontamination occurring when the sheet is peeled (hereinafter, referredto as a contamination property) is little. The contamination property ofthe pressure-sensitive adhesive sheet is evaluated in accordance withthe method and conditions described in the later-described Examples.

The pressure-sensitive adhesive sheet of the present embodiment hascharacteristics that: the pressure-sensitive adhesive force, occurringat the beginning of attachment, is as low as rework can be performed;thereafter the sheet is firmly adhered to an adherend; and furthercontamination is little when the sheet is peeled. Accordingly, thepressure-sensitive adhesive sheet can be preferably used: in opticalapplications in which optical films to be used in image displayapparatuses, such as a liquid crystal display, plasma display, andorganic EL display, are adhered, etc.; and also as materials for joiningmembers in mobile devices and other electrical and electronic equipment,etc., or as materials for joining various members in automobiles andhome electronic appliances, etc.

EXAMPLES

Hereinafter, examples of the present invention will be described, whichdo not intend to limit the scope of the invention at all, but arepresented as exemplifications for preferably describing the invention.

(Preparation of Acrylic Polymer Syrup 1 (2EHA/NVP=86/14) as (A)Component)

Eighty six parts by mass of 2-ethylhexyl acrylate (2EHA), 14 parts bymass of N-vinyl-2-pyrrolidone (NVP), 0.05 parts by mass of aphoto-polymerization initiator (product name: IRGACURE 184, made byBASF), and 0.05 parts by mass of a photo-polymerization initiator(product name: IRGACURE 651, made by BASF) were placed into a 4-neckflask. A partial polymer (acrylic polymer syrup) having a polymerizationrate of approximately 8% by mass was obtained by exposing the mixture toultraviolet rays under a nitrogen atmosphere to be partiallyphotopolymerized.

(Preparation of Acrylic Polymer Syrup 2 (2EHA/AA=94/6) as (A) Component)

Ninety four parts by mass of 2-ethylhexyl acrylate (2EHA), 6 parts bymass of acrylic acid (AA), 0.05 parts by mass of a photo-polymerizationinitiator (product name: IRGACURE 184, made by BASF), and 0.05 parts bymass of a photo-polymerization initiator (product name: IRGACURE 651,made by BASF) were placed into a 4-neck flask. A partial polymer(acrylic polymer syrup) having a polymerization rate of approximately 8%by mass was obtained by exposing the mixture to ultraviolet rays under anitrogen atmosphere to be partially photopolymerized.

(Preparation of (Meth)acrylic Polymer 1 (MMA/BMA/2 EHMA/X-22-174ASX/X-22-174DX=40/20/20/17/3) as (B) Component)

One hundred parts by mass of toluene, 40 parts by mass of methylmethacrylates (MMA), 20 parts by mass of butyl methacrylate (BMA), 20parts by mass of 2-ethylhexyl methacrylate (2-EHMA), 17 parts by mass ofa methacrylate monomer having a functional group equivalent of 900 g/moland containing a polyorganosiloxane skeleton (product name: X-22-174ASX,made by Shin-Etsu Chemical Co., Ltd.), 3 parts by mass of a methacrylatemonomer having a functional group equivalent of 4600 g/mol andcontaining a polyorganosiloxane skeleton (product name: X-22-174DX, madeby Shin-Etsu Chemical Co., Ltd.), and 0.51 parts by mass of methylthioglycolate as a chain transfer agent were placed into a 4-neck flaskprovided with a stirring blade, thermometer, nitrogen gas inlet pipe,cooler, and dropping funnel. After they were stirred under a nitrogenatmosphere at 70° C. for 1 hour, 0.2 parts by mass ofazobisisobutyronitrile were placed therein as a thermal polymerizationinitiator to react with them at 70° C. for 2 hours. Thereafter, 0.1parts by mass of azobisisobutyronitriles were placed therein as athermal polymerization initiator to subsequently react with them at 80°C. for 5 hours. The weight average molecular weight of the obtained(meth)acrylic polymer 1 was 22800.

((Meth)Acrylic Polymer as Another (B) Component)

Each of (Meth)acrylic Polymers 2 to 11 was produced in the same way as(Meth)acrylic Polymer 1, except that a monomer composition, the type ofa solvent, and the parts by mass of a chain transfer agent were added inthe way described in Table 1.

TABLE 1 COPOLYMERIZATION No. COMPOSITION RATIO (METH)ACRYLIC POLYMER 1MMA/BMA/2EHMA/X22-174ASX/X22-174DX 40/20/20/17/3 (METH)ACRYLIC POLYMER 2MMA/BMA/2EHMA/X22-174ASX/X22-174DX 40/20/20/14/6 (METH)ACRYLIC POLYMER 3MMA/BMA/2EHMA/X22-174ASX/X22-174DX 40/20/20/8.7/11.3 (METH)ACRYLICPOLYMER 4 MMA/BMA/2EHMA/X22-174DX 40/20/20/20 (METH)ACRYLIC POLYMER 5MMA/BMA/2EHMA/X22-174DX 40/20/20/20 (METH)ACRYLIC POLYMER 6DCPMA/BMA/2EHMA/X22-174DX 40/20/20/20 (METH)ACRYLIC POLYMER 7DCPMA/2EHMA/X22-174DX 40/40/20 (METH)ACRYLIC POLYMER 8MMA/BMA/2EHMA/X22-174DX 45/22.5/22.5/10 (METH)ACRYLIC POLYMER 9X22-174DX (HOMOPOLYMER) 100 (METH)ACRYLIC POLYMER 10 X22-174ASX(HOMOPOLYMER) 100 (METH)ACRYLIC POLYMER 11 MMA/BMA/2EHMA/X22-174ASX40/20/20/20 NON- (METH)ACRYLIC POLYMER 12 KF-96-100cs (LINEAR SILICONE)— NON- (METH)ACRYLIC POLYMER 13 KF-96H-10 

 CS (LINEAR SILICONE) — NON- (METH)ACRYLIC POLYMER 14 X22-174DX(MACROMONOMER) — NON- (METH)ACRYLIC POLYMER 15 X22-174ASX (MACROMONOMER)— CHAIN TRANSFER FUNCTIONAL AGENT (METHYL GROUP THIOGLYCOLATE) No.EQUIVALENT PARTS BY MASS SOLVENT Mw (METH)ACRYLIC POLYMER 1 1460 0.51TOLUENE 22800 (METH)ACRYLIC POLYMER 2 2010 0.51 TOLUENE 22400(METH)ACRYLIC POLYMER 3 2990 0.51 TOLUENE 22500 (METH)ACRYLIC POLYMER 44600 0.51 TOLUENE 24100 (METH)ACRYLIC POLYMER 5 4600 0.45 TOLUENE 35600(METH)ACRYLIC POLYMER 6 4600 0.51 TOLUENE 19000 (METH)ACRYLIC POLYMER 74600 0.51 TOLUENE 18200 (METH)ACRYLIC POLYMER 8 4600 0.53 TOLUENE 22200(METH)ACRYLIC POLYMER 9 4600 0 N-HEPTANE 41000 (METH)ACRYLIC POLYMER 10900 0 TOLUENE 480000 (METH)ACRYLIC POLYMER 11 900 0.55 TOLUENE 21700NON- (METH)ACRYLIC POLYMER 12 — — — 8000 NON- (METH)ACRYLIC POLYMER 13 —— — 100000 NON- (METH)ACRYLIC POLYMER 14 4600 — — — NON- (METH)ACRYLICPOLYMER 15 900 — — —

The abbreviations described in Table 1 are as follows.

-   -   MMA: methyl methacrylate Tg 105° C.    -   BMA: BUTYL METHACRYLATE Tg 20° C.    -   2EHMA: 2-ethylhexyl methacrylate Tg −10° C.    -   X-22-174ASX: methacrylate monomer containing a        polyorganosiloxane skeleton and having a functional group        equivalent of 900 g/mol, made by Shin-Etsu Chemical Co., Ltd.    -   X-22-174DX: methacrylate monomer containing a polyorganosiloxane        skeleton and having a functional group equivalent of 4600 g/mol,        made by Shin-Etsu Chemical Co., Ltd.    -   KF-96-100cs: silicone oil (linear silicone) having a        polydimethylsiloxane structure, kinematic viscosity 100 mm²/s        (25° C.), made by Shin-Etsu Chemical Co., Ltd.    -   KF-96-100,000cs: silicone oil (linear silicone) having a        polydimethylsiloxane structure, kinematic viscosity 100,000        mm²/s (25° C.), made by Shin-Etsu Chemical Co., Ltd.

<Measurement of Molecular Weight>

The weight average molecular weight of a polymer was measured by using aGPC apparatus (product name: HLG-8220GPC, made by TOSOH CORP.).Measurement conditions were as follows and the molecular weight wasdetermined by standard polystyrene conversion.

-   -   Sample concentration: 0.2 wt % (tetrahydrofuran (THF) solution)    -   Sample injection volume: 10 μl    -   Eluent: THF    -   Flow Rate: 0.6 ml/min    -   Measuring temperature: 40° C.    -   Column:        -   Sample column; TSKguardcolumn SuperHZ-H (one column1)+TSKgel            SuperHZM-H (two columns)        -   Reference column; TSKgel SuperH-RC (one column)    -   Detector: differential refractometer (RI)

Example 1 (Preparation of Pressure-Sensitive Adhesive Composition)

After 5 parts by mass of the aforementioned (meth)acrylic polymer 1 and0.1 parts by mass of trimethylolpropane triacrylate (TMPTA) as across-linking agent were added to 100 parts by mass of theaforementioned acrylic polymer syrup 1, these were mixed uniformly toprepare a pressure-sensitive adhesive composition.

(Production of Pressure-Sensitive Adhesive Layer)

A coated layer having a final thickness of 50 μm was formed by coatingthe aforementioned pressure-sensitive adhesive composition on onesurface of a polyester film having a thickness of 38 μm (product name:Diafoil MRF, made by Mitsubishi Plastics Inc.), the one surface havingbeen subjected to a release treatment with silicone. Subsequently, thesurface of the coated pressure-sensitive adhesive composition wascovered with one surface of a polyester film having a thickness of 38 μm(product name: Diafoil MRE, made by Mitsubishi Plastics Inc.), the onesurface having been subjected to a release treatment with silicone, sothat the one surface of the film was located near to the coated layer.Thereby, oxygen was blocked from the coated layer of thepressure-sensitive adhesive composition (pressure-sensitive adhesivecomposition layer). A pressure-sensitive adhesive layer sheet wasobtained by irradiating, for 360 seconds, the coated layer thus obtainedwith ultraviolet rays having an illuminance of 5 mW/cm² (measured byTOPCONUVR-T1 having a maximum sensitivity at approximately 350 nm) withthe use of a chemical light lamp (made by TOSHIBA CORPORATION) in orderto polymerize the composition. The polyester films provided on both thesurfaces of the pressure-sensitive adhesive layer sheet function as arelease liner.

Examples 2 to 20, Comparative Examples 1 to 17

Each of the pressure-sensitive adhesive layer sheets of Examples 2 to 20and Comparative Examples 1 to 17 was prepared in the same way as that ofExample 1 by preparing a pressure-sensitive adhesive composition in thesame way as Example 1, except that the polymer (B) and the use amountthereof listed in Table 2 were used based on 100 parts by mass of thepolymer (A) listed in Table 1.

TABLE 2 CROSS-LINKING AGENT POLYMER (B) (POLYFUNCTIONAL GEL POLYMER (A)100 PART BY MONOMER) FRACTION PARTS BY MASS TYPE MASS PART BY MASS (%)EXAMPLE 1 2EHA/NVP = 86/14 (METH)ACRYLIC POLYMER 1 5 0.1 87.0 EXAMPLE 22EHA/NVP = 86/14 (METH)ACRYLIC POLYMER 2 3 0.08 85.1 EXAMPLE 3 2EHA/NVP= 86/14 (METH)ACRYLIC POLYMER 2 5 0.1 87.0 EXAMPLE 4 2EHA/NVP = 86/14(METH)ACRYLIC POLYMER 2 10 0.1 84.4 EXAMPLE 5 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 2 3 0.07 73.9 EXAMPLE 6 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 2 5 0.09 82.5 EXAMPLE 7 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 2 10 0.09 76.2 EXAMPLE 8 2EHA/NVP = 86/14(METH)ACRYLIC POLYMER 3 3 0.08 84.6 EXAMPLE 9 2EHA/NVP = 86/14(METH)ACRYLIC POLYMER 3 5 0.1 86.6 EXAMPLE 10 2EHA/NVP = 86/14(METH)ACRYLIC POLYMER 3 10 0.1 85.4 EXAMPLE 11 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 3 3 0.07 76.4 EXAMPLE 12 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 3 5 0.09 77.5 EXAMPLE 13 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 3 10 0.09 79.5 EXAMPLE 14 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 4 1 0.07 77.4 EXAMPLE 15 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 4 3 0.08 79.6 EXAMPLE 16 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 4 5 0.09 81.2 EXAMPLE 17 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 5 5 0.09 81.6 EXAMPLE 18 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 6 5 0.1 82.1 EXAMPLE 19 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 7 5 0.1 81.5 EXAMPLE 20 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 8 5 0.09 78.6 COMPARATIVE 2EHA/NVP = 86/14 — —0.06 84.2 EXAMPLE 1 COMPARATIVE 2EHA/AA = 94/6 — — 0.09 83.5 EXAMPLE 2COMPARATIVE 2EHA/NVP = 86/14 NON-(METH)ACRYLIC 5 0.1 87.9 EXAMPLE 3POLYMER 12 COMPARATIVE 2EHA/NVP = 86/14 NON-(METH)ACRYLIC 10 0.1 84.7EXAMPLE 4 POLYMER 12 COMPARATIVE 2EHA/NVP = 86/14 NON-(METH)ACRYLIC 10.07 83.2 EXAMPLE 5 POLYMER 13 COMPARATIVE 2EHA/NVP = 86/14NON-(METH)ACRYLIC 5 0.1 89.3 EXAMPLE 6 POLYMER 13 COMPARATIVE 2EHA/NVP =86/14 NON-(METH)ACRYLIC 1 0.07 85.0 EXAMPLE 7 POLYMER 14 COMPARATIVE2EHA/NVP = 86/14 NON-(METH)ACRYLIC 5 0.1 88.8 EXAMPLE 8 POLYMER 14COMPARATIVE 2EHA/NVP = 86/14 NON-(METH)ACRYLIC 5 0.1 88.6 EXAMPLE 9POLYMER 15 COMPARATIVE 2EHA/NVP = 86/14 (METH)ACRYLIC POLYMER 9 1 0.0786.6 EXAMPLE 10 COMPARATIVE 2EHA/NVP = 86/14 (METH)ACRYLIC POLYMER 9 50.1 89.1 EXAMPLE 11 COMPARATIVE 2EHA/NVP = 86/14 (METH)ACRYLIC POLYMER10 1 0.07 87.9 EXAMPLE 12 COMPARATIVE 2EHA/NVP = 86/14 (METH)ACRYLICPOLYMER 10 5 0.1 92.0 EXAMPLE 13 COMPARATIVE 2EHA/AA = 94/6(METH)ACRYLIC POLYMER 10 5 0.1 82.6 EXAMPLE 14 COMPARATIVE 2EHA/NVP =86/14 (METH)ACRYLIC POLYMER 11 1 0.07 85.1 EXAMPLE 15 COMPARATIVE2EHA/NVP = 86/14 (METH)ACRYLIC POLYMER 11 5 0.1 86.9 EXAMPLE 16COMPARATIVE 2EHA/AA = 94/6 (METH)ACRYLIC POLYMER 11 5 0.09 75.6 EXAMPLE17

Example 21 (Preparation of Acrylic Polymer 1 as (A) Component bySolution Polymerization)

Five parts by mass of acrylic acid, 95 parts by mass of 2-ethylhexylacrylate, and 200 parts by mass of ethyl acetate as a polymerizationsolvent were placed into a 4-neck flask provided with a stirring blade,thermometer, nitrogen gas inlet pipe, and cooler. After they werestirred under a nitrogen atmosphere at 60° C. for 2 hours, 0.2 parts bymass of azobisisobutyronitrile were placed therein as a thermalpolymerization initiator to react with them at 60° C. for 6 hours. Theweight average molecular weight of the obtained polymer was 1,100,000.

(Preparation of Pressure-Sensitive Adhesive Composition)

A pressure-sensitive adhesive composition (1) was prepared: by adding,to 500 parts by mass of a solution (100 parts by mass of the acrylicpolymer (A)) in which the aforementioned acrylic polymer (A) solution(35% by mass) was diluted with ethyl acetate to 20% by mass, 3 parts bymass of the (meth)acrylic polymer 2, 1 part by mass of CORONATE L (anadduct of trimethylolpropane/tolylene diisocyanate trimer, made byNIPPON POLYURETHANE INDUSTRY CO., LTD.) as a cross-linking agent, and 3parts by mass of an ethyl acetate solution (1% by mass) of dioctyl tindilaurate as a cross-linking catalyst; and then by mixing and stirringthem at 25° C. for approximately 5 minutes.

(Production of Pressure-Sensitive Adhesive Sheet) A pressure-sensitiveadhesive layer having a thickness of

50 μm was formed: by coating the aforementioned pressure-sensitiveadhesive composition (1) on one surface of a polyester film having athickness of 38 μm (product name: Diafoil MRF, made by MitsubishiPlastics Inc.), the one surface having been subjected to a releasetreatment with silicone; and then by heating the composition (1) at 130°C. for approximately 2 minutes.

Examples 22, 23, 29 to 32, Comparative Example 18

Each of the pressure-sensitive adhesive layer sheets of Examples 22, 23,29 to 32 and Comparative Example 18 was prepared in the same way as thatof Example 21 by preparing a pressure-sensitive adhesive composition inthe same way as Example 21, except that the polymer (B) and the useamount thereof listed in Table 3 were used based on 100 parts by mass ofthe polymer (A) listed in Table 1. In Example 29, 20 parts by mass of atackifying resin with the product name of “SUMILITE RESIN PR-12603N”(made by SUMITOMO BAKELITE CO., LTD.) were used. In Example 30, 20 partsby mass of a tackifying resin with the product name of “PENSEL D-125”(made by ARAKAWA CHEMICAL INDUSTRIES, LTD.) were used. In Example 31, 20parts by mass of a tackifying resin with the product name of “TAMANOL803L” (made by ARAKAWA CHEMICAL INDUSTRIES, LTD.) were used. In Example32, 20 parts by mass of a tackifying resin with the product name of “YSPolystar N125” (made by YASUHARA CHEMICAL CO., LTD.) were used.

Examples 24 to 28, Comparative Example 19 (Preparation of AcrylicPolymer 2 as (A) Component by Solution Polymerization)

Five parts by mass of acrylic acid, 100 parts by mass of n-butylacrylate, and 200 parts by mass of toluene as a polymerization solventwere placed into a 4-neck flask provided with a stirring blade,thermometer, nitrogen gas inlet pipe, and cooler. After they werestirred under a nitrogen atmosphere at 60° C. for 2 hours, 0.2 parts bymass of azobisisobutyronitrile were placed therein as a thermalpolymerization initiator to react with them at 60° C. for 6 hours. Theweight average molecular weight of the obtained polymer was 400,000. Thepressure-sensitive adhesive composition (1) was prepared by using theacrylic polymer 2 in the same way as the aforementioned Example 21, andthen a pressure-sensitive adhesive sheet was produced.

TABLE 3 CROSS- LINKING AGENT POLYMER (B) (CORONATE L) GEL POLYMER (A)100 PARTS PARTS BY FRACTION PARTS BY MASS TYPE BY MASS MASS (%) EXAMPLE21 2EHA/AA = 95/5 (METH)ACRYLIC POLYMER 2 3 1 47.0 EXAMPLE 22 2EHA/AA =95/5 (METH)ACRYLIC POLYMER 2 5 1 47.7 EXAMPLE 23 2EHA/AA = 95/5(METH)ACRYLIC POLYMER 3 3 1 45.0 EXAMPLE 24 BA/AA = 100/5 (METH)ACRYLICPOLYMER 2 3 1 32.8 EXAMPLE 25 BA/AA = 100/5 (METH)ACRYLIC POLYMER 3 3 133.8 EXAMPLE 26 BA/AA = 100/5 (METH)ACRYLIC POLYMER 3 5 1 33.7 EXAMPLE27 BA/AA = 100/5 (METH)ACRYLIC POLYMER 4 1 1 34.4 EXAMPLE 28 BA/AA =100/5 (METH)ACRYLIC POLYMER 4 3 1 33.5 EXAMPLE 29 2EHA/AA = 95/5(METH)ACRYLIC POLYMER 3 5 1 32.1 EXAMPLE 30 2EHA/AA = 95/5 (METH)ACRYLICPOLYMER 3 5 3 39.1 EXAMPLE 31 2EHA/AA = 95/5 (METH)ACRYLIC POLYMER 3 5 127.0 EXAMPLE 32 2EHA/AA = 95/5 (METH)ACRYLIC POLYMER 3 5 1 27.3COMPARATIVE 2EHA/AA = 95/5 — — 1 51.1 EXAMPLE 18 COMPARATIVE BA/AA =100/5 — — 1 32.9 EXAMPLE 19

(Measurement of Ratio of Solvent-Insoluble Component)

A ratio of a solvent-insoluble component (gel fraction) was calculatedin the following way: after 0.1 g of a pressure-sensitive adhesivecomposition was sampled and precisely weighed (mass before dipping), thesampled composition was dipped in approximately 50 ml of ethyl acetateat room temperature (20 to 25° C.) for 1 week; a solvent (ethyl acetate)insoluble component was taken out to be dried at 130° C. for 2 hours andthen weighed (mass after dipping and drying); and the ratio wascalculated by using an equation for calculating a “ratio ofsolvent-insoluble component (% by mass)=[(mass after dipping anddrying)/(mass before dipping)]×100”. The results of measuring the ratiosof solvent-insoluble components are shown in Tables 2 and 3.

(Test Method) [180°-Peeling Pressure-Sensitive Adhesive Force Test]

After the release liner (polyester film) on one surface of the acrylicpressure-sensitive adhesive layer sheet according to each of Examplesand Comparative Examples was peeled, a polyethylene terephthalate filmhaving a thickness of 50 μm was attached. The obtained sheet was cutinto a piece having a width of 25 mm, which was used as a test specimen.A glass plate having a thickness of 1.2 mm (made by Matsunami GlassInd., Ltd.), which had been cleaned with isopropyl alcohol, an ABSplate, and a stainless plate (430BA), which had been cleaned withtoluene, were provided. After the release liner (polyester film) on theother surface of the pressure-sensitive adhesive layer sheet was peeled,the pressure-sensitive adhesive surface of the sheet was attached to thestainless plate (430BA plate), the ABS plate, and a glass plate,respectively, by reciprocating a 2-kg roller.

After the pressure-sensitive adhesive layer sheets were attached to thestainless plate (430BA plates), the ABS plate, and the glass plate,respectively, the plates were left under an environment of 23° C. for 30minutes (initial condition). Additionally, after the pressure-sensitiveadhesive layer sheets were attached to the stainless plate (430BAplate), the ABS plate, and the glass plate, respectively, and then after48 hours elapsed under an environment of 40° C., the plates were leftunder an environment of 23° C. for 30 minutes (ordinary condition). Theother end of each of the pressure-sensitive adhesive layer sheets ineach of the initial condition and the ordinary condition was peeled inthe 180°-peeling direction at a speed of 300 mm/min. Thepressure-sensitive adhesive force (resistance force) (unit: N/25 mm) tothe adherend, occurring at the time, was measured. With respect to allthe three adherends, the case was determined to be good (°) where thepressure-sensitive adhesive force in the initial condition was smallerthan 7.0 and the pressure-sensitive adhesive force in the ordinarycondition was two times or more larger than that in the initialcondition; and the case was determined to be bad (X) where the force inthe initial condition was 7.0 or more and the force in the ordinarycondition was less than two times the force in the initial condition.Results of measuring the 180°-peeling pressure-sensitive adhesive forceare shown in Tables 4 and 5.

[Contamination Property]

After the release liner (polyester film) on one surface of thepressure-sensitive adhesive layer sheet according to each of Examplesand Comparative Examples was peeled, a polyethylene terephthalate filmhaving a thickness of 50 μm was attached. The obtained sheet was cutinto apiece having a width of 25 mm, which was used as a test specimen.A stainless plate (430BA) having a thickness of 0.42 mm, which had beencleaned with toluene, was provided. After the release liner (polyesterfilm) on the other surface of the pressure-sensitive adhesive layersheet was peeled, the pressure-sensitive adhesive surface of the sheetwas attached to the stainless plate (430BA plate) by reciprocating a2-kg roller. Then, the attached sheet was left under an atmosphere of23° C. and a relative humidity of 50% for 30 minutes, and the externalappearance of the adherend was observed after the pressure-sensitiveadhesive layer sheet was peeled in the 180° direction at a speed of 300mm/min. The case was evaluated to be good (°) where contamination wasnot confirmed at all, while the case was evaluated to be bad (X) wherecontamination was confirmed. Results of evaluating contaminationproperties are shown in Tables 4 and 5.

TABLE 4 PRESSURE- PRESSURE- PRESSURE- SENSITIVE ADHESIVE SENSITIVEADHESIVE SENSITIVE ADHESIVE FORCE TO SUS FORCE TO ABS FORCE TO GLASS(430BA) (N/25 mm) (N/25 mm) (N/25 mm) REWORK + AFTER AFTER AFTERINCREASING TWO DAYS TWO DAYS TWO DAYS CONTAMINATION PROPERTY INITIAL AT40° C. INITIAL AT 40° C. INITIAL AT 40° C. PROPERTY OVER TIME EXAMPLE 13.9 10.8 5.0 12.8 3.5 11.3 ∘ ∘ EXAMPLE 2 4.5 11.5 3.7 10.8 3.9 10.7 ∘ ∘EXAMPLE 3 2.6 10.3 3.7 11.3 2.8 10.2 ∘ ∘ EXAMPLE 4 3.0 11.7 3.2 11.8 1.711.5 ∘ ∘ EXAMPLE 5 2.9 16.5 2.7 16.3 4.5 17.7 ∘ ∘ EXAMPLE 6 0.7 12.0 0.716.5 3.8 18.0 ∘ ∘ EXAMPLE 7 0.3 12.0 0.3 13.7 0.9 16.9 ∘ ∘ EXAMPLE 8 4.210.1 3.4 10.0 3.1 9.0 ∘ ∘ EXAMPLE 9 3.0 8.9 1.6 10.0 1.8 8.2 ∘ ∘ EXAMPLE10 1.8 10.2 1.6 10.0 1.3 9.5 ∘ ∘ EXAMPLE 11 1.7 10.9 1.3 14.9 3.1 16.2 ∘∘ EXAMPLE 12 0.3 8.3 0.4 11.8 2.3 14.4 ∘ ∘ EXAMPLE 13 0.3 9.3 0.3 10.80.5 14.6 ∘ ∘ EXAMPLE 14 2.7 6.6 3.4 12.7 2.8 11.0 ∘ ∘ EXAMPLE 15 0.9 5.62.2 7.0 1.9 8.5 ∘ ∘ EXAMPLE 16 1.5 6.4 1.1 7.0 1.4 7.5 ∘ ∘ EXAMPLE 171.2 5.7 0.7 8.2 2.5 7.4 ∘ ∘ EXAMPLE 18 1.0 5.7 0.7 6.3 0.8 4.3 ∘ ∘EXAMPLE 19 1.4 7.3 1.1 8.3 0.9 6.1 ∘ ∘ EXAMPLE 20 2.4 8.8 3.4 14.1 3.811.8 ∘ ∘ COMPARATIVE 11.0 10.9 9.8 12.5 9.1 11.4 ∘ x EXAMPLE 1COMPARATIVE 12.4 16.7 12.3 14.8 14.4 15.2 ∘ x EXAMPLE 2 COMPARATIVE 5.29.7 5.9 10.2 4.7 8.5 x x EXAMPLE 3 COMPARATIVE 5.3 8.6 5.6 9.5 4.4 6.5 xx EXAMPLE 4 COMPARATIVE 8.3 10.5 8.6 13.3 9.0 11.5 x x EXAMPLE 5COMPARATIVE 5.2 4.2 5.1 8.8 4.6 4.3 x x EXAMPLE 6 COMPARATIVE 9.3 11.08.2 11.8 4.9 9.7 ∘ x EXAMPLE 7 COMPARATIVE 6.7 8.9 6.1 10.3 2.4 6.1 x xEXAMPLE 8 COMPARATIVE 9.5 10.4 8.9 12.0 7.6 9.9 x x EXAMPLE 9COMPARATIVE 5.8 9.0 4.7 10.6 3.1 7.9 x x EXAMPLE 10 COMPARATIVE 0.7 1.71.0 1.0 0.4 0.8 x x EXAMPLE 11 COMPARATIVE 9.6 11.3 8.9 12.0 7.5 9.7 ∘ xEXAMPLE 12 COMPARATIVE 7.0 9.4 6.1 9.3 3.6 5.2 x x EXAMPLE 13COMPARATIVE 4.5 8.3 4.5 12.7 6.7 9.1 x x EXAMPLE 14 COMPARATIVE 9.6 12.110.2 14.6 11.2 13.2 ∘ x EXAMPLE 15 COMPARATIVE 8.0 10.2 8.6 16.0 9.110.7 ∘ x EXAMPLE 16 COMPARATIVE 9.5 15.9 11.8 19.1 15.1 23.2 ∘ x EXAMPLE17

TABLE 5 PRESSURE- PRESSURE- PRESSURE- SENSITIVE ADHESIVE SENSITIVEADHESIVE SENSITIVE ADHESIVE FORCE TO SUS FORCE TO ABS FORCE TO GLASS(430BA) (N/25 mm) (N/25 mm) (N/25 mm) REWORK + AFTER AFTER AFTERINCREASING TWO DAYS TWO DAYS TWO DAYS CONTAMINATION PROPERTY INITIAL AT40° C. INITIAL AT 40° C. INITIAL AT 40° C. PROPERTY OVER TIME EXAMPLE 210.17 8.2 0.41 9.9 0.80 7.5 ∘ ∘ EXAMPLE 22 0.12 8.2 0.13 10.0 0.28 7.2 ∘∘ EXAMPLE 23 0.14 5.1 0.28 7.9 0.37 5.7 ∘ ∘ EXAMPLE 24 0.89 7.6 0.98 9.92.50 9.2 ∘ ∘ EXAMPLE 25 0.72 8.2 0.76 10.1 4.80 10.6 ∘ ∘ EXAMPLE 26 0.125.5 0.14 7.0 0.32 5.8 ∘ ∘ EXAMPLE 27 0.84 8.6 1.52 10.1 4.30 10.4 ∘ ∘EXAMPLE 28 0.26 7.9 0.23 9.4 2.40 4.9 ∘ ∘ EXAMPLE 29 0.16 2.6 0.15 4.90.30 5.3 ∘ ∘ EXAMPLE 30 0.35 5.0 2.90 8.2 1.40 5.0 ∘ ∘ EXAMPLE 31 0.144.6 1.35 7.2 0.20 5.5 ∘ ∘ EXAMPLE 32 0.38 4.5 1.80 6.6 0.45 4.8 ∘ ∘COMPARATIVE 10.10 9.7 10.10 12.4 8.40 10.1 ∘ x EXAMPLE 18 COMPARATIVE9.00 10.0 9.80 13.5 9.30 11.8 ∘ x EXAMPLE 19

The present invention should not be limited to the aforementionedembodiments, and various modifications, such as design modifications,can be made with respect to the above embodiments based on the knowledgeof those skilled in the art, and an embodiment with such a modificationcan fall within the scope of the invention.

For example, matters disclosed by this description include thefollowing:

(1) A pressure-sensitive adhesive composition comprising:

-   -   an acrylic polymer (A) having a glass transition temperature        lower than 0 C.°; and    -   a polymer (B) containing, as monomer units, both a monomer (B1)        having a polyorganosiloxane skeleton and a monomer (B2) whose        homopolymer has a glass transition temperature of 40 C.° or        higher;    -   wherein the acrylic polymer (A) contains, as a monomer unit, at        least one monomer selected from the group consisting of N-vinyl        cyclic amides represented by the following general formula (M1):

wherein R¹ is a divalent organic group.

(2) The pressure-sensitive adhesive composition according to (1) above,wherein a content of the monomer selected from the group consisting ofN-vinyl cyclic amides is 0.01% by mass to 40% by mass, based on thetotal monomer components of the polymer (A).

(3) The pressure-sensitive adhesive composition according to (1) or (2)above, wherein a content of the monomer (B1) is 5% by mass or more but50% by mass or less, based on the total monomer components of thepolymer (B).

(4) The pressure-sensitive adhesive composition according to any of (1)to (3) above, wherein

-   -   the monomer (B2) comprises a monomer whose homopolymer has a        glass transition temperature of 80 C.° or higher, and    -   a content of the monomer whose homopolymer has a glass        transition temperature of 80 C.° or higher is 10% by mass or        more but 80% by mass or less, based on the total monomer        components of the polymer (B).

(5) The pressure-sensitive adhesive composition according to any of (1)to (4) above, wherein the total monomer components of the polymer (B)comprise:

-   -   15% by mass or more but 30% by mass or less of the monomer (B1),        and    -   10% by mass or more but 80% by mass or less of a monomer whose        homopolymer has a glass transition temperature of 80 C.° or        higher, as the monomer (B2).

(6) The pressure-sensitive adhesive composition according to any of (1)to (5) above, wherein the monomer (B2) comprises both a monomer whosehomopolymer has a glass transition temperature of 80 C.° or higher and amonomer whose homopolymer has a glass transition temperature of 40 C.°or higher but lower than 80 C.°.

(7) The pressure-sensitive adhesive composition according to any of (1)to (6) above, wherein the monomer having a polyorganosiloxane skeletonis one or more monomers selected from the group consisting of monomersrepresented by the following general formula (1) or (2):

wherein, R₃ is hydrogen or methyl; R₄ is methyl or a monovalent organicgroup; and each of m and n is an integer of 0 or more.

(8) The pressure-sensitive adhesive composition according to any of (1)to (7) above, further comprising a polymerization initiator.

(9) A pressure-sensitive adhesive sheet comprising a pressure-sensitiveadhesive layer made of a pressure-sensitive adhesive composition,wherein

-   -   the pressure-sensitive adhesive composition includes:        -   an acrylic polymer (A) having a glass transition temperature            lower than 0 C.°; and    -   a polymer (B) containing, as monomer units, both a monomer (B1)        having a polyorganosiloxane skeleton and a monomer (B2) whose        homopolymer has a glass transition temperature of 40 C.° or        higher;    -   wherein the acrylic polymer (A) contains, as a monomer unit, at        least one monomer selected from the group consisting of N-vinyl        cyclic amides represented by the following general formula (M1):

wherein R¹ is a divalent organic group.

(10) The pressure-sensitive adhesive sheet according to (9) above,wherein the pressure-sensitive adhesive sheet is provided on at leastone surface of a supporting body.

(11) The pressure-sensitive adhesive sheet according to (9) or (10)above,

-   -   wherein pressure-sensitive adhesive force to each of a stainless        plate, an ABS plate, and a glass plate, occurring in an initial        condition of 23° C. for 30 minutes, is smaller than 3.0 N/25 mm,        and wherein    -   pressure-sensitive adhesive force to each of the plates,        occurring in an ordinary condition of 48 hours at 40° C.,        followed by 23° C. for 30 minutes, is 5.7 times or more larger        than the pressure-sensitive adhesive force occurring in the        initial condition.

(12) A pressure-sensitive adhesive composition comprising:

-   -   an acrylic polymer (A) having a glass transition temperature        lower than 0 C.°; and    -   a polymer (B) containing, as monomer units, both a monomer (B1)        having a polyorganosiloxane skeleton and a monomer (B2) whose        homopolymer has a glass transition temperature of 40 C.° or        higher;    -   wherein the acrylic polymer (A) contains, as a monomer unit, at        least one monomer selected from the group consisting of N-vinyl        cyclic amides represented by the following general formula (M1):

wherein R¹ is a divalent organic group;

-   -   wherein a content of the monomer selected from the group        consisting of N-vinyl cyclic amides is 0.01% by mass to 40% by        mass, based on the total monomer components of the polymer (A),    -   the total monomer components of the polymer (B) comprise:        -   15% by mass or more but 30% by mass or less of the monomer            (B1), and        -   10% by mass or more but 80% by mass or less of a            (meth)acrylic monomer whose homopolymer has a glass            transition temperature of 80 C.° or higher, as the monomer            (B2),    -   the monomer (B2) comprises both a (meth)acrylic monomer whose        homopolymer has a glass transition temperature of 80 C.° or        higher and a (meth)acrylic monomer whose homopolymer has a glass        transition temperature of 40 C.° or higher but lower than 80        C.°.

(13) The pressure-sensitive adhesive sheet comprising apressure-sensitive adhesive layer formed from the pressure-sensitiveadhesive composition according to any of (1) to (8) and (12).

(14) The pressure-sensitive adhesive composition comprising:

-   -   a polymer (A) having a glass transition temperature lower than 0        C.°; and    -   a polymer (B) containing, as monomer units, both a monomer (B1)        having a polyorganosiloxane skeleton.

(15) The pressure-sensitive adhesive composition according to (14)above, wherein the monomer having a polyorganosiloxane skeleton is oneor more monomers selected from the group consisting of monomersrepresented by the following general formula (1) or (2):

wherein, R₃ is hydrogen or methyl; R₄ is methyl or a monovalent organicgroup; and each of m and n is an integer of 0 or more.

(16) The pressure-sensitive adhesive composition according to (14) or(15) above, wherein the content of the monomer having apolyorganosiloxane skeleton is 5% by mass or more and 50% by mass orless, based on the mass of the total monomer components of the polymer(B).

(17) The pressure-sensitive adhesive composition according to any of(14) to (16) above, wherein the monomer components for preparing thepolymer (B) contains the monomer having a polyorganosiloxane skeletonand a monomer whose homopolymer has a glass transition temperature of 40C.° or higher.

(18) The pressure-sensitive adhesive composition according to (17)above, wherein the monomer components for preparing the polymer (B)contains, as the monomer whose homopolymer has a glass transitiontemperature of 40 C.° or higher, a monomer whose homopolymer has a glasstransition temperature of 80 C.° or higher, and a monomer whosehomopolymer has a glass transition temperature of 40 C.° or higher andlower than 80 C.° in combination.

(19) The pressure-sensitive adhesive composition according to any of(14) to (18) above, wherein the monomer components for preparing thepolymer (B) contains the monomer having a polyorganosiloxane skeletonand a (meth)acrylic monomer.

(20) The pressure-sensitive adhesive composition according to (19)above, wherein a (meth)acrylic monomer contains a (meth)acrylic monomerwhose homopolymer has a glass transition temperature of 40 C.° orhigher.

(21) The pressure-sensitive adhesive composition according to (19)above, wherein a (meth)acrylic monomer contains a (meth)acrylic monomerwhose homopolymer has a glass transition temperature of 80 C.° orhigher.

(22) The pressure-sensitive adhesive composition according to (21)above, wherein the content of the (meth)acrylic monomer whosehomopolymer has a glass transition temperature of 80 C.° or higher is30% by mass or more and 50 mass % or less, is based on the mass of thetotal monomer components of the polymer (B).

(23) The pressure-sensitive adhesive composition according to (21) or(22) above, wherein the (meth)acrylic monomer further contains a(meth)acrylic monomer whose homopolymer has a glass transitiontemperature of lower than 80 C.°.

(24) The pressure-sensitive adhesive composition according to any of(14) to (23) above, wherein the polymer (A) is an acrylic polymer.

(25) The pressure-sensitive adhesive composition according to (24)above, wherein the acrylic polymer contains, as monomer units, both amonomer selected from the group consisting of the N-vinyl cyclic amidesand a monomer selected from hydroxyl group-containing monomers.

(26) The pressure-sensitive adhesive composition according to any of(14) to (25) above, wherein the content of the polymer (B) is 0.1 to 20parts by mass, based on 100 parts by mass of the polymer (A).

(27) The pressure-sensitive adhesive sheet comprising apressure-sensitive adhesive layer formed from the pressure-sensitiveadhesive composition according to any of (14) to (26) above.

(28) The pressure-sensitive adhesive sheet according to (13) or (27)above, wherein

-   -   pressure-sensitive adhesive force to each of a stainless plate,        an ABS plate, and a glass plate, occurring in an initial        condition of 23° C. for 30 minutes, is smaller than 3.0 N/25 mm,        and wherein    -   pressure-sensitive adhesive force to each of the plates,        occurring in an ordinary condition of 48 hours at 40° C.,        followed by 23° C. for 30 minutes, is 5.7 times or more larger        than the pressure-sensitive adhesive force occurring in the        initial condition.

The present invention can be used, for example, in metal adherends andadherends on which a metal film is formed.

What is claimed is:
 1. A pressure-sensitive adhesive compositioncomprising: an acrylic polymer (A) having a glass transition temperaturelower than 0 C.°; and a polymer (B) containing, as monomer units, both amonomer (B1) having a polyorganosiloxane skeleton and a monomer (B2)whose homopolymer has a glass transition temperature of 40 C.° orhigher; wherein the acrylic polymer (A) contains, as a monomer unit, atleast one monomer selected from the group consisting of N-vinyl cyclicamides represented by the following general formula (M1):

wherein R¹ is a divalent organic group.
 2. The pressure-sensitiveadhesive composition according to claim 1, wherein a content of themonomer selected from the group consisting of N-vinyl cyclic amides is0.01% by mass to 40% by mass, based on the total monomer components ofthe polymer (A).
 3. The pressure-sensitive adhesive compositionaccording to claim 1, wherein a content of the monomer (B1) is 5% bymass or more but 50% by mass or less, based on the total monomercomponents of the polymer (B).
 4. The pressure-sensitive adhesivecomposition according to claim 1, wherein the monomer (B2) comprises amonomer whose homopolymer has a glass transition temperature of 80 C.°or higher, and a content of the monomer whose homopolymer has a glasstransition temperature of 80 C.° or higher is 10% by mass or more but80% by mass or less, based on the total monomer components of thepolymer (B).
 5. The pressure-sensitive adhesive composition according toclaim 1, wherein the total monomer components of the polymer (B)comprises: 15% by mass or more but 30% by mass or less of the monomer(B1), and 10% by mass or more but 80% by mass or less of a monomer whosehomopolymer has a glass transition temperature of 80 C.° or higher, asthe monomer (B2).
 6. The pressure-sensitive adhesive compositionaccording to claim 1, wherein the monomer (B2) comprises both a monomerwhose homopolymer has a glass transition temperature of 80 C.° or higherand a monomer whose homopolymer has a glass transition temperature of 40C.° or higher but lower than 80 C.°.
 7. The pressure-sensitive adhesivecomposition according to claim 1, wherein the monomer having apolyorganosiloxane skeleton is one or more monomers selected from thegroup consisting of monomers represented by the following generalformula (1) or (2):

wherein, R₃ is hydrogen or methyl; R₄ is methyl or a monovalent organicgroup; and each of m and n is an integer of 0 or more.
 8. Thepressure-sensitive adhesive composition according to claim 1, furthercomprising a polymerization initiator.
 9. A pressure-sensitive adhesivesheet comprising a pressure-sensitive adhesive layer made of apressure-sensitive adhesive composition, wherein the pressure-sensitiveadhesive composition includes: an acrylic polymer (A) having a glasstransition temperature lower than 0 C.°; and a polymer (B) containing,as monomer units, both a monomer (B1) having a polyorganosiloxaneskeleton and a monomer (B2) whose homopolymer has a glass transitiontemperature of 40 C.° or higher; wherein the acrylic polymer (A)contains, as a monomer unit, at least one monomer selected from thegroup consisting of N-vinyl cyclic amides represented by the followinggeneral formula (M1).

wherein R¹ is a divalent organic group.
 10. The pressure-sensitiveadhesive sheet according to claim 9, wherein the pressure-sensitiveadhesive sheet is provided on at least one surface of a supporting body.11. The pressure-sensitive adhesive sheet according to claim 9, whereinpressure-sensitive adhesive force to each of a stainless plate, an ABSplate, and a glass plate, occurring in an initial condition of 23° C.for 30 minutes, is smaller than 3.0 N/25 mm, and whereinpressure-sensitive adhesive force to each of the plates, occurring in anordinary condition of 48 hours at 40° C., followed by 23° C. for 30minutes, is 5.7 times or more larger than the pressure-sensitiveadhesive force occurring in the initial condition.
 12. Apressure-sensitive adhesive composition comprising: an acrylic polymer(A) having a glass transition temperature lower than 0 C.°; and apolymer (B) containing, as monomer units, both a monomer (B1) having apolyorganosiloxane skeleton and a monomer (B2) whose homopolymer has aglass transition temperature of 40 C.° or higher; wherein the acrylicpolymer (A) contains, as a monomer unit, at least one monomer selectedfrom the group consisting of N-vinyl cyclic amides represented by thefollowing general formula (M1):

wherein R¹ is a divalent organic group; wherein a content of the monomerselected from the group consisting of N-vinyl cyclic amides is 0.01% bymass to 40% by mass, based on the total monomer components of thepolymer (A), the total monomer components of the polymer (B) comprise:15% by mass or more but 30% by mass or less of the monomer (B1), and 10%by mass or more but 80% by mass or less of a (meth)acrylic monomer whosehomopolymer has a glass transition temperature of 80 C.° or higher, asthe monomer (B2), the monomer (B2) comprises both a (meth)acrylicmonomer whose homopolymer has a glass transition temperature of 80 C.°or higher and a (meth)acrylic monomer whose homopolymer has a glasstransition temperature of 40 C.° or higher but lower than 80 C.°.